118 ELEMENTARY STUDIES IN BOTANY 



leaves (Fig. 94). Sometimes the trunks are short, resem- 

 bling casks or large tubers, but they always bear the crown 

 of fern-like leaves. 



There are two other living groups, very much scattered, 

 and very few in numbers, so that they need not be described. 



The pine will be used as a representative of Gymnosperms, 

 since it is a conspicuous and familiar form. 



69. The sporophyte. The pine " tree " is of course 

 a sporophyte that has become very large (Fig. 93). The 

 vascular cylinder of the stem is thick, and it becomes thicker 

 each year by adding new layers of wood. This continual 

 increase in the amount of water-conducting tissue makes wide 

 and continued branching possible, for branching means an 

 increase in leaf display, and increased leaf display means 

 a larger supply of water not only for food manufacture, but 

 chiefly to supply the loss from the leaves. The tree type 

 of body, with its tall trunk and spreading branches bearing 

 a great mass of foliage, is the most advanced type of 

 sporophyte body. In other words, it is the sporophyte 

 at its best. 



In the pine the leaves are not broad, being only green 

 " needles," but they are very numerous (Fig. 95). There 

 are Conifers, however, with broad leaves, and the Cycads 

 have very large fern-like leaves (Fig. 94). 



70. The strobili. A pine tree bears two kinds of strobili 

 (" cones "), but many Gymnosperms have the two kinds of 

 strobili on different trees. The pine cone that is ordinarily 

 seen is the strobilus that bears megasporangia ; that is, it is 

 a group of megasporophylls. It is so much larger and more 

 persistent than the other kind that to most people it seems 

 to be the only kind of cone on the tree. But there are also 

 small strobili composed of groups of microsporophylls bear- 

 ing microsporangia (Fig. 95). 



Ovulate strobilus. If one of the larger cones of the pine 

 is cut through lengthwise (Fig. 96, A), it will be found to 



