Part 28 (2/2)
Intermediates were not seen, and as the plant bore some pods, it was possible to test its constancy. I raised about 500 plants from its seeds, out of which more than 100 flowered in the first year. The others were partly kept through the winter and flowered next year. Seeds saved in [588] both seasons were sown on a large scale. Both the first and the succeeding generations of the offspring of the original plant came true without any exception. Intermediates are often found in hybrid cultures, and in them the character is a very variable one, but as yet they were not met with in progeny of this mutant. All these plants were exactly like _O. biennis_, with the single exception of their petals.
_Epilobium hirsutum cruciatum_ was discovered by John Rasor near Woolpit, Bury St. Edmunds, in England. It flowered in one spot, producing about a dozen stems, among large quant.i.ties of the parent-species, which is very common there, as it is elsewhere in Europe. This species is a perennial, multiplying itself by underground runners, and the stems of the new variety were observed to stand so close to each other that they might be considered as the shoots of one individual. In this case this specimen might probably be the original mutant, as the variety had not been seen on that spot in previous years, even as it has not been found elsewhere in the vicinity.
Intermediates were not observed, though the difference is a very striking one. In the cruciate flowers the broad and bright purple petals seem at first sight to be wholly wanting. They are too weak to expand and to reflex the calyx [589] as in the normal flowers of the species.
The sepals adhere to one another, and are only opened at their summit by the protruding pistils. Even the stamens hardly come to light. At the period of full bloom the flowers convey only the idea of closed buds crowned by the conspicuous white cross of the stigma. Any intermediate form would have at once betrayed itself by larger colored petals, coming out of the calyx-sheath. The cruciate petals are small and linear and greenish, recalling thereby the color of the sepals.
Mr. Rasor having sent me some flowers and some ripe capsules of his novelty, I sowed the latter in my experimental garden, where the plant flowered in large numbers and with many thousands of flowers both in 1902 and 1903. All of these plants and all of these flowers repeated the cruciate type exactly, and not the slightest impurity or tendency to partial reversion has been observed.
Thus true and constant cruciate varieties have been produced from accidentally observed initial plants, and because of their very curious characters they will no doubt be kept in botanical gardens, even if they should eventually become lost in their native localities.
At this point I might note another observation made on the wild species of _Oenothera cruciata_ [590] from the Adirondacks. Through the kindness of Dr. MacDougal, of the New York Botanical Garden, I received seeds from Sandy Hill near Lake George. When the plants, grown from these seeds, flowered, they were not a uniform lot, but exhibited two distinct types. Some had linear petals and thin flower-buds, and in others the petals were a little broader and the buds more swollen. The difference was small, but constant on all the flowers, each single plant clearly belonging to one or the other of the two types. Probably two elementary species were intermixed here, but whether one is the systematic type and the other a mutation, remains to be seen.
Nor seem these two types to exhaust the range of variability of _Oenothera cruciata_. Dr. B.L. Robinson of Cambridge, Ma.s.s., had the kindness to send me seeds from another locality in the same region. The seeds were collected in New Hamps.h.i.+re and in my garden produced a true and constant _cruciata_, but with quite different secondary characters from both the aforesaid varieties. The stems and flower-spikes and even the whole foliage were much more slender, and the calyx-tubes of the flowers were noticeably more elongated. It seems not improbable that _Oenothera cruciata_ includes a group of lesser unities, and may prove to comprise a [591] swarm of elementary species, while the original strain might even now be still in a condition of mutability. A close scrutiny in the native region is likely to reveal many unexpected features.
A very interesting novelty has already been described in a former lecture. It is the _Xanthium wootoni_, discovered in the region about Las Vegas, New Mexico, by T.D.A. c.o.c.kerell. It is similar in all respects to _X. commune_, but the burrs are more slender and the p.r.i.c.kles much less numerous, and mostly stouter at their base. It grows in the same localities as the _X. commune_, and is not recorded to occur elsewhere. Whether it is an old variety or a recent mutation it is of course impossible to decide. In a culture made in my garden from the seed sent me by Mr. c.o.c.kerell, I observed (1903) that both forms had a subvariety with brownish foliage, and, besides this, one of a pure green. Possibly this species, too, is still in a mutable condition.
Perhaps the same may be a.s.serted concerning the beautiful shrub, _Hibiscus Moscheutos_, observed in quite a number of divergent types by John W. Harshberger. They grew in a small meadow at Seaside Park, New Jersey, in a locality which had been undisturbed for years. They differed from each other in nearly all the [592] organs, in size, in the diameter of the stems, which were woody in some and more fleshy in others, in the shape of the foliage and in the flowers. More than twenty types could be distinguished and seeds were saved from a number of them, in order to ascertain whether they are constant, or whether perhaps a main stem in a mutating condition might be found among them. If this should prove to be the case, the relations between the observed forms would probably be a.n.a.logous to those between the _O. lamarckiana_ and its derivatives.
Many other varieties have sprung from the type-species under similar conditions from time to time. A fern-leaved mercury, _Mercurialis annua laciniata_, was discovered in the year 1719 by Marchant. The type was quite new at the time and maintained itself during a series of years.
The yellow deadly nightshade or _Atropa Belladonna lutea_ was found about 1850 in the Black Forest in Germany in a single spot, and has since been multiplied by seeds. It is now dispersed in botanical gardens, and seems to be quite constant. A dwarf variety of a bean, _Phaseolus lunatus_, was observed to spring from the ordinary type by a sudden leap about 1895 by W.W. Tracy, and many similar cases could be given.
The annual habit is not very favorable for [593] the discovery of new forms in the wild state. New varieties may appear, but may be crowded out the first year. The chances are much greater with perennials, and still greater with shrubs or trees. A single aberrant specimen may live for years and even for centuries, and under such conditions is pretty sure to be discovered sooner or later. Hence it is no wonder that many such cases are on record. They have this in common that the original plant of the variety has been found among a vast majority of representatives of the corresponding species. Nothing of course is directly known about its origin. Intermediate links have as a rule been wanting, and the seeds, which have often been sown, have not yielded reliable results, as no care was taken to preserve the blossoms from intercrossing with their parent-forms.
Stress should be laid upon one feature of these curious occurrences.
Relatively often the same novelty has been found twice or thrice, or even more frequently, and under conditions which make it very improbable that any relation between such occurrences might exist. The same mutation must have taken place more than once from the same main stem.
The most interesting of these facts are connected with the origin of the purple beech, which [594] is now so universally cultivated. I take the following statements from an interesting historical essay of Prof.
Jaggi. He describes three original localities. One is near the Swiss village, Buch am Irchel, and is located on the Stammberg. During the 17th century five purple beeches are recorded to have grown on this spot. Four of them have died, but one is still alive. Seedlings have germinated around this little group, and have been mostly dug up and transplanted into neighboring gardens. Nothing is known about the real origin of these plants, but according to an old doc.u.ment, it seems that about the year 1190 the purple beeches of Buch were already enjoying some renown, and attracting large numbers of pilgrims, owing to some old legend. The church of Embrach is said to have been built in connection with this legend, and was a goal for pilgrimages during many centuries.
A second native locality of the purple beech is found in a forest near Sondershausen in Thuringen, Germany, where a fine group of these trees is to be seen. They were mentioned for the first time in the latter half of the eighteenth century, but must have been old specimens long before that time. The third locality seems to be of much later origin. It is a forest near Roveredo in South Tyrol, where a new [595] university is being erected. It is only a century ago that the first specimens of the purple beech were discovered there.
As it is very improbable that the two last named localities should have received their purple beeches from the first named forest, it seems reasonable to a.s.sume that the variety must have been produced at least thrice.
The purple beech is now exceedingly common in cultivation. But Jaggi succeeded in showing that all the plants owe their origin to the original trees mentioned above, and are, including nearly all cultivated specimens with the sole exception of the vicinity of Buch, probably derived from the trees in Thuringen. They are easily multiplied by grafting, and come true from seed, at least often, and in a high proportion. Whether the original trees would yield a pure progeny if fertilized by their own pollen has as yet not been tested. The young seedlings have purple seed-leaves, and may easily be selected by this character, but they seem to be always subjected in a large measure to vicinism.
Many other instances of trees and shrubs, found in accidental specimens const.i.tuting a new variety in the wild state, might be given. The oak-leaved beech has been found in a forest of Lippe-Detmold in Germany and near Versailles, [596] whence it was introduced into horticulture by Carriere. Similarly divided and cleft leaves seem to have occurred more often in the wild state, and cut-leaved hazels are recorded from Rouen in France, birches and alders from Sweden and Lapland, where both are said to have been met with in several forests. The purple barberry was found about 1830 by Bertin, near Versailles. Weeping varieties of ashes were found wild in England and in Germany, and broom-like oaks, _Quercus pedunculata fastigiata_, are recorded from Hessen-Darmstadt, Calabria, the Pyrenees and other localities. About the real origin of all these varieties nothing is definitely known.
The ”single-leaved” strawberry is a variety often seen in botanical gardens, as it is easily propagated by its runners. It was discovered wild in Lapland at the time of Linnaeus, and appeared afterwards unexpectedly in a nursery near Versailles. This happened about the year 1760 and d.u.c.h.esne tested it from seeds and found it constant. This strain, however, seems to have died out before the end of the 18th century. In a picture painted by Holbein (1495-1543), strawberry leaves can be seen agreeing exactly with the monophyllous type. The variety may thus be a.s.sumed to have arisen independently [597] at least thrice, at different periods and in distant localities.
From all these statements and a good many others which can be found in horticultural and botanical literature, it may be inferred that mutations are not so very rare in nature as is often supposed. Moreover we may conclude that it is a general rule that they are neither preceded nor accompanied by intermediate steps, and that they are ordinarily constant from seed from the first.
Why then are they not met with more often? In my opinion it is the struggle for life which is the cause of this apparent rarity; which is nothing else than the premature death of all the individuals that so vary from the common type of their species as to be incapable of development under prevailing circ.u.mstances. It is obviously without consequence whether these deviations are of a fluctuating or of a mutating nature. Hence we may conclude that useless mutations will soon die out and will disappear without leaving any progeny. Even if they are produced again and again by the same strain, but under the same unfavorable conditions, there will be no appreciable result.
Thousands of mutations may perhaps take place yearly among the plants of our immediate vicinity without any chance of being discovered. [598] We are trained to the appreciation of the differentiating marks of systematic species. When we have succeeded in discerning these as given by our local flora lists, we rest content. Meeting them again we are in the habit of greeting them with their proper names. Such is the satisfaction ensuing from this knowledge that we do not feel any inclination for further inquiry. Striking deviations, such as many varietal characters, may be remarked, but then they are considered as being of only secondary interest. Our minds are turned from the delicately shaded features which differentiate elementary species.
Even in the native field of the evening-primroses, no botanist would have discovered the rosettes with smaller or paler leaves, const.i.tuting the first signs of the new species. Only by the guidance of a distinct theoretical idea were they discovered, and having once been pointed out a closer inspection soon disclosed their number.
Variability seems to us to be very general, but very limited. The limits however, are distinctly drawn by the struggle for existence. Of course the chance for useful mutations is a very small one. We have seen that the same mutations are as a rule repeated from time to time by the same species. Now, if a useful mutation, [599] or even a wholly indifferent one, might easily be produced, it would have been so, long ago, and would at the present time simply exist as a systematic variety. If produced anew somewhere the botanist, would take it for the old variety and would omit to make any inquiry as to its local origin.
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