Part 11 (1/2)

In the Pteridophytes, however, we find that the sporogonium becomes very much more developed, and finally beco in round, after which it e size

The sexual plant, which is here called the ”prothalliu the lower liverworts usually, and never reaches more than about a centimetre in diameter, and is often much smaller than this

The codom, and a careful study of any of these will illustrate the principal peculiarities of the group The whole plant, as we know it, is really nothing but the sporogoniu cell in exactly the saives rise to spores which are formed upon the leaves

The sporesleaves on sheets of paper and letting the the paper as a fine, broder If these are sown on fine, rather closely packed earth, and kept lass so as to prevent evaporation, within a week or two a fine, green, roill make its appearance, and by the end of five or six weeks, if the weather is warreen color may be seen These look like small liverworts, and are the sexual plants (prothallia) of our ferns (Fig 66, _F_) Re one of these carefully, we find on the lower side numerous fine hairs like those on the lower surface of the liverworts, which fasten it firround By and by, if our culture has been successful, we er of these, little fern plants growing froround by a delicate root As the little plant becoround as an independent plant, which after a time bears the spores

[Illustration: FIG 66--_A_, spore of the ostrich fern (_Onoclea_), with the outer coat re prothallium, 50 _r_, root hair _sp_ spore membrane _D_, _E_, older prothallia _a_, apical cell, 150 _F_, a feonia _G_, _H_, young archegonia, in optical section, 150 _o_, central cell _b_, ventral canal cell

_c_, upper canal cell _I_, a ripe archegoniu cell _J_, aantheridia, in optical section, 300 _M_, ripe antheridium, 300 _sp_ spered their contents, 300 _P_, spermatozoids, killed with iodine, 500 _v_, vesicle attached to the hinder end]

In choosing spores for gere size and containing abundant chlorophyll, as they germinate more readily Especially favorable for this purpose are the spores of the ostrich fern (_Onoclea struthiopteris_) (Fig 70, _I_, _J_), or the sensitive fern (_O sensibilis_) Another corown species is the lady fern (_Aspleniu 70, _H_) The spores of most ferns retain their vitality for many months, and hence can be kept dry until wanted

The first stages of ger the spores in water, where, under favorable circuroithin three or four days The outer, dry, brown coat of the spore is first ruptured, and often co of the spore contents Below this is a second colorless membrane which is also ruptured, but reh the orifice in the second coat, the inner delicate membrane protrudes in the forates and becomes separated fro the first root hair (Fig 66, _B_, _C_, _r_) The body of the spore containing ates more slowly, and divides by a series of transverse walls so as to for in structure soae (_C_)

In order to follow the development further, spores must be sown upon earth, as they do not develop norrown on earth, they should be carefully removed and washed in a drop of water so as to remove, as far as possible, any adherent particles, and then may be mounted in water for microscopic examination

In most cases, after three or four cross-walls are formed, talls arise in the end cell so inclined as to enclose a wedge-shaped cell (_a_) fro 66, _D_, _E_, _a_), the apical cell growing to its original diments divide by vertical walls in various directions so that the young plant rapidly assuround by root hairs developed froinal ones As the division walls are all vertical, the plant is nowhere ments divide more rapidly than the inner ones, and soon project beyond the apical cell which thus comes to lie at the bottom of a cleft in the front of the plant which in consequence becomes heart-shaped (_E_, _F_) Sooner or later the apical cell ceases to foruishable from the other cells

In the ostrich fern and lady fern the plants are dicious The66, _J_) are very s thickly form dense, ularly shaped, others sier plants

The fee and regularly heart-shaped, occasionally reaching a diameter of nearly or quite one centinizable without microscopical examination

All the cells of the plant except the root hairs contain large and distinct chloroplasts much like those in the leaves of the moss, and like theonia arise from cells of the lower surface, just behind the notch in front (Fig 66, _F_, _ar_) Previous to their formation the cells at this point divide by walls parallel to the surface of the plant, so as to form several layers of cells, and froonia arise They resemble those of the liverworts but are shorter, and the lower part is co 66, _G_, _I_)

They arise as single surface cells, this first dividing into three by walls parallel to the outer surface The lower cell undergoes one or two divisions, but undergoes no further change; the second cell (_C_, _o_), beco cell, and from it is cut off another cell (_c_), the canal cell of the neck; the uppermost of the three becomes the neck There are four rows of neck cells, the two forward ones being longer than the others, so that the neck is bent backward In the full-grown archegonium, there are two canal cells, the lower one (_H_, _b_) called the ventral canal cell, being soniuanized in the same way as in the bryophytes, and the protoplas cell which shows a large, central nucleus, and in favorable cases, a clear space at the top called the ”receptive spot,” as it is here that the spermatozoid enters When ripe, if placed in water, the neck cells become very much distended and finally open widely at the top, the upper ones not infrequently being detached, and the re 66, _I_)

The antheridia (Fig 66 _J_, _M_) arise as simple hemispherical cells, in which talls are formed (_K_ I, II), the lower funnel-shaped, the upper he the lower one so as to enclose a central cell (shaded in the figure), fro-shaped wall (_L_ iii) is for off a sort of cap cell, so that the antheridiue consists of a central cell, surrounded by three other cells, the ter ring-shaped, the upper disc-shaped The central cell, which contains dense, glistening protoplasm, is destitute of chlorophyll, but the outer cells have a few small chloroplasts The former divides repeatedly, until arise to a large spirally-coiled spermatozoid When ripe, the mass of sperm cells crowds so upon the outer cells as to render them almost invisible, and as they ripen they separate by a partial dissolving of the division walls When brought into water, the outer cells of the antheridiuly, and the matter derived from the dissolved walls of the sperm cells also absorbs water, so that finally the pressure becoreat that the wall of the antheridiu up of the wall cells (_N_, _O_) After lying a few moments in the water, the wall of each sperm cell becomes completely dissolved, and the sper movement They may be killed with a little iodine, when each is seen to be a somewhat flattened band, coiled several times At the forward end, the coils are s and delicate cilia At the hinder enda few sranules, so blue when iodine is applied

In studying the development of the antheridia, it is only necessary to mount the plants in water and exaonia requires careful longitudinal sections of the prothallium To make these, the prothallium should be placed between small pieces of pith, and the razor must be very sharp It may be necessary to use a little potash to h to see the structure, but this reat delicacy of the tissues

If a plant with ripe archegonia is placed in a drop of water, with the lower surface uppermost, and at the same time male plants are put with it, and the whole covered with a cover glass, the archegonia and antheridia will open simultaneously; and, if examined with the microscope, we shall see the speronia, to which they are attracted by the substance forced out when it opens With a little patience, one or h which it forces itself, by a sloistingcell In order to make the experiment successful, the plants should be allowed to beco taken that no water is poured over them for a day or two beforehand

The first divisions of the fertilized egg cell resemble those in the moss eoniules to it Very soon, however, the e established instead of the single one found in thepoints on the side of the erow faster than the others, one of these outstripping the other, and soon beco 67, _A_, _L_) The other (_r_) is peculiar, in having its growing point covered by several layers of cells, cut off from its outer face, a peculiarity which we shall find is characteristic of the roots of all the higher plants, and, indeed, this is the first root of the young fern Of the other two growing points, the one next the leaf grows slowly, for a blunt cone (_st_), and is the apex of the stem The other (_f_) has no definite foran of absorption, by means of which nourishment is supplied to the embryo from the prothallium; it is known as the foot

[Illustration: FIG 67--_A_, eh the prothallium, 50 _st_ apex of steoniu plant, still attached to the prothalliuround ste leaf, and the base of an older one, 1 _D_, three cross-sections of a leaf stalk: i, nearest the base; iii, nearest the blade of the leaf, showing the division of the fibro-vascular bundle, 5 _E_, part of the blade of the leaf,_F_, a single spore-bearing leaflet, showing the edge folded over to cover the sporangia, 1 _G_, part of the fibro-vascular bundle of the leaf stalk (cross-section), 50

_x_, woody part of the bundle _y_, bast _sh_ bundle sheath _H_, a small portion of the saround steround stem, 300]