GENERAL MOEPHOLOGY OF THE PLANT 15 



the plant, however, is none the less constant or important in the 

 former group, though it never attains any considerable size. 



If we compare the forms of the gametophyte and sporophyte 

 in such plants as plainly possess both, we can notice that the 

 gametophyte is usually a thallus, but is oormophytic in the larger 

 Algae, the Jungermannias, a family of the Liverworts, and in 

 the Mosses. The sporophyte is a thallus in such of the Algae and 

 Fungi as possess one, but with few exceptions it is a cormophyte 

 in all plants above the Mosses. In the higher plants it thus 

 presents us with a series of members. We may distinguish the 

 root and the shool ; the latter including various forms of branches 

 and different kinds of leaves. Its most important members are 

 the stem, the vegetative branches, the inflorescence, and the 

 flowers ; the leaves, some foliage leaves, others sporophylU ; 

 lastly the fruit and seed. 



The gametophyte is seen at its best in the AlgiE, Fungi, 

 Liverworts, and Mosses. Here it may show root, stem, and leaf, 

 or it may be only a thallus or a thalloid shoot. Above the 

 Mosses it is gradually and progressively reduced, being never 

 more than a thaUus above this point, and gradually becoming 

 less and less prominent, till at last it consists of only a few 

 cells in the interior of the megaspore. 



The several members of the plant may now be considered 

 in greater detail separately, the morphology of the special 

 reproductive members being deferred to a succeeding chapter. 



Thallophytes. 

 The Thallus. 



The thallus may consist of a single cell, or may be composed 

 of many cells. It shows scarcely any distinction of parts or 

 segmentation, and but little differentiation of its internal tissues. 

 Allien composed of more than one cell it may be a filament or a 

 collection of filaments, or a flat plate often onlj' one cell thick, or 

 a mass of some size. In the last two cases it may bear a num- 

 ber of hairs from any part of its surface. In some cases, as in 

 Volooj--, it is a spherical body capable of active movement 

 carried out by special filaments or cilia, «'hioh move rapidly to 

 and fro in the water in which the plant li^'es. It may be 

 branched, certain branches being like the main body, and 

 others specially modified to produce the reproductive organs. 



The thallus is seen best in the lowest plants, where generally 

 the whole plant body is of this description. It is the prominent 



