Part 13 (1/2)

The second order (_Ligulatae_) is represented by two very distinct fainelleae_) and the quill-worts (_Isoeteae_) Of the forreenhouses where they are prized for their delicate74, _A_)

[Illustration: FIG 74--_A_, one of the s branch, 2 _B_, part of a steitudinal section of a spike, with a single ia, 3 _D_, a scale and ium, 150 The shaded cells are the sporele fibro-vascular bundle, 150 _I_, vertical section of the feoniu cell _K_, microspore, with the contained etative cell _sp_ sper plant, with the attached macrospore, 6 _r_, the first root _l_, the first leaves]

The leaves in er club ed in four rows on the upper side of the sterow out sideways so that the whole branch appears flattened, reher liverworts Special leafless branches (_B_, _r_) often groard froround develop roots which fork regularly

The sporangia are ly at the bases of scale leaves arranged in a spike or cone (_A_, _sp_), but two kinds of spores, large and siue spores (macrospores); the others, numerous small spores (microspores)

Even before the spores are ripe the developnificant, as it shows an undoubted relationshi+p between these plants and the lowest of the seed plants, as we shall see e study that group

If ripe spores can be obtained by sowing the plants will appear in about a74, _K_) produces a prothalliu a single vegetative cell (_x_), and the rest of the prothalliule antheridium The spermatozoids are excessively small, and resemble those of the bryophytes

The e lower one, and a sives rise to a flat disc of cells producing a nu 74, _I_, _J_) The lower cell produces later a tissue that serves to nourish the young embryo

The development of the embryo recalls in some particulars that of the seed plants, and this in connection with the peculiarities of the sporangia warrants us in regarding the _Ligulatae_ as the highest of existing pteridophytes, and to a certain extent connecting the the s in some important points, are the quill-worts (_Isoeteae_) They are ed, and look like grasses or rushes They vary froht The ste cylindrical leaves closely crowded together The leaves which are narrow above are widely expanded and overlapping at the base The spores are of two kinds, as in _Selaginella_, but the e sporangia (_M_, _sp_) are in cavities at the bases of the leaves, and above each sporangiuula), which is also found in the leaves of _Selaginella_ The quill-worts are not corowth and resemblance to other plants, are likely to be overlooked unless careful search is made

CHAPTER XIV

SUB-KINGDOM VI

SPERMAPHYTES: PHaeNOGAMS

The last and highest great division of the vegetable kingdom has been named _Spermaphyta_, ”seed plants,” from the fact that the structures known as seeds are peculiar to theh this naher pteridophytes

In the seed plants the ia remain attached to the parent plant, in nearly all cases, until the archegonia are fertilized and the eium now becoher sper leaves (sporophylls) beco thethe ia are also ordinarily known as ”ovules,” a naiven before it was known that these were the saher pteridophytes

In addition to the spore-bearing leaves, those surrounding the, with the enclosed sporophylls, the ”flower” of the higher sperher sperh some of them are very si little floating plants, less than a antic trees, a hundred ht

There are two classes of the spermaphytes: I, the Gymnosperia) are borne upon open carpophylls; and II, Angiosperms, covered-seeded plants, in which the carpophylls for the ovules

CLass I--GYMNOSPERMS (_Gymnospermae_)

The reen trees (conifers), pines, spruces, cedars, etc A careful study of one of these will give a good idea of the most important characteristics of the class, and one of the best for this purpose is the Scotch pine (_Pinus sylvestris_), which, though a native of Europe, is not infrequently met with in cultivation in America If this species cannot be had by the student, other pines, or indeed almost any other conifer, will answer The Scotch pine is a tree of , with a central ular intervals; but as it grows older its growth becoular, and the crown is divided into several main branches[10] The trunk and branches are covered with a rough, scaly bark of a reddish brown color, where it is exposed by the scaling off of the outer layers Covering the younger branches, but beco thinner on the older ones, are numerous needle-shaped leaves These are in pairs, and the base of each pair is surrounded by several dry, blackish scales Each pair of leaves is really attached to a very short side branch, but this is so short as to row directly froth and two millimetres broad Where the leaves are in contact they are flattened, but the outer side is rounded, so that a cross-section is nearly semicircular in outline With a lens it is seen that there are five longitudinal lines upon the surface of the leaf, and careful exa to these These dots are the breathing pores If a cross-section is even slightly nified it shows three distinct parts,--a whitish outer border, a bright green zone, and a central oval, colorless area, in which, with a little care, may be seen the sections of two fibro-vascular bundles In the green zone are sometimes to be seen colorless spots, sections of resin ducts, containing the resin so characteristic of the tissues of the conifers

[10] Intree is eneral structure of the ste a series of cross-sections through branches of different ages In all, three regions are distinguishable; viz, an outer region (bark or cortex) (Fig 76, _A_, _c_), coreen cells, and, if the section has been s, froe resin ducts (_r_) The centre is occupied by a soft white tissue (pith), and the space between the pith and bark is filled by athe wood are nu lines, some of which run from the bark to the pith, others only part way These are called the e these three regions are recognizable, their relative size varies extre of the present year the bark and pith make up a considerable part of the section; but as older branches are examined, we find a rapid increase in the quantity of wood, while the thickness of the bark increases but slowly, and the pith scarcely at all In the wood, too, each year's growth is row in diaular, and portions die, beco brown and hard

The tree has a very perfect root system, but different from that of any pteridophytes The first root of the erown tree, and froive rise to others