]^Y4 PLANT STRUCTURES 



95. The plant body. — The great body of the plant, often 

 forming a large tree, is the sporophyte ; in fact, the 

 gametophytes are not visible to ordinary observation. It 

 should be remembered that the sporophyte is distinctly a 

 sexless generation, and that it develops no sex organs. 

 This great sporophyte body is elaborately organized for 

 nutritive work, with its roots, stems, and leaves. These 

 organs are very complex in structure, being made up of 

 various tissue systems that are organized for special kinds 

 of work. The leaves are the most variable organs, being 

 differentiated into three distinct kinds — (1) foliage leaves, 

 (2) scales, and (3) sporophylls. 



96. Sporophylls. — The sporophylls are leaves set apart to 

 produce sporangia, and in the pine they are arranged in 

 a strobilus, as in the Horsetails and Club-mosses. As 

 the group is heterosporous, however, there are two kinds 

 of sporophylls and two kinds of strobili. One kind of 

 strobilus is made up of megasporophylls bearing mega- 

 sporangia ; the other is made up of microsporophylls bear- 

 ing microsporangia. These strobili are often spoken of as 

 the "flowers" of the jDine, but if these are flowers, so are 

 the strobili of Horsetails and Club-mosses. 



97. Microsporophylls. — In the pines the strobilus com- 

 posed of microsporophylls is comparatively small (Figs. 

 145, d, 164). Each sporophyll is like a scale leaf, is nar- 

 rowed at the base, and upon the lower surface are borne 

 two prominent sporangia, which of course are microspo- 

 rangia, and contain microspores (Fig. 146). 



These structures of Seed-plants all received names 

 before they were identified with the corresponding struc- 

 tures of the lower groups. The microsporophyll was called a 

 stamen, the microsporangia j)ollen-sacs, and the microspores 

 foUen grains, or simply pollen. These names are still very 

 convenient to use in connection with the Spermatophytes, 

 but it should be remembered that they are simply other 

 names for structures found in the lower groups. 



