THE PLANT-BODY 



19 



different from those of the Ferns or Flowering Plants, they have 

 undoubtedly arisen in response to the same needs, and perform the 

 same function. They are, in short, analogous, but not homologous, 

 organs. 



A similar transition from the thallose to the leafy shoot is found 

 among the Mosses, where there are many interesting forms interme- 

 diate between a flat thallus and a true leafy shoot (Fig. 9, B). 



Vascular Plants 



It is among the so-called Vascular Plants, i.e. Ferns and 

 Flowering Plants, that the most perfect 

 development of the plant-body is found. 

 The gametophyte or plant which bears 

 the sexual reproductive cells is always 

 a very simple thallus in these plants ; 

 but from the egg there is developed a 

 very complicated plant (Sporophyte), 

 which produces non-sexual spores only. 

 It is the sporophyte only, in these 

 plants, which exhibits the great variety 

 of structure that is associated with 

 the vascular plants, which are now the 

 predominant plant-types. 



In the typical vascular plant (Fig. 

 10), the sporophyte is clearly differ- 

 entiated into a root, which serves the 

 double purpose of attachment and 

 absorption, and the shoot, which con- 

 sists of the stem and the leaves. The 

 root is at first a direct continuation 

 of the shoot, but it may be replaced by 

 secondary roots, and, like the shoot, 

 it is capable of branching. 



The Shoot. In all but aquatic plants 

 the shoot develops a complicated sys- 

 tem of "mechanical tissues," which 

 give it the requisite rigidity to main- 

 tain its upright position in the air. 



These mechanical tissues in the leaves Fio 10 ._ Seedling of a Morning . 

 also give the necessary support to the glory, a vascular plant with 

 spread-out masses of delicate green highly developed stem, root, and 

 cells. From the main shoot may be leaves ' a^tiy reduced, 

 developed secondary shoots, resulting in an extensive branch system. 



Besides the leaves and branches, there are developed from the 



