156 Plant Life and Evolution 



usually united into a compound structure, the pistil 

 (Fig. i8,D). 



The apocarpous flowers are generally admitted to 

 be primitive types, but whether all of the diclinous 

 flowers are reduced from such types, having both 

 stamens and carpels, is another question. It seems 

 more in accordance with the data at hand to assume 

 that in the primitive angiospermous stock there were 

 developed both monosporangiate and amphisporan- 

 giate flowers. From these two types of flowers in 

 the primitive angiosperms, the similar types of flow- 

 ers, as we now find them in both monocotyledons 

 and dicotyledons, may very well have directly arisen. 



Fertilization in Angiosperms. The peculiar posi- 

 tion of the ovules of the angiosperms, protected 

 within the ovary, involves special adaptations for 

 insuring fertilization. Instead of the pollen coming 

 into contact directly with the ovule, as it does in 

 the Gymnosperms, it falls upon the variously modi- 

 fied upper portion of the pistil, the stigma 

 (Fig. 1 6, A). This is specially fitted to retain the 

 pollen and to facilitate its germination, but the 

 germination of the pollen itself is very similar to 

 that of the gymnosperms. After germination the 

 pollen-tube must traverse the whole length of the 

 pistil before it finally reaches the ovules. The inter- 

 mediate portion of the pistil, or " style," is usually 

 cylindrical in form, and the central tissue is espe- 

 cially modified so as to form a special conducting 

 tissue which nourishes the rapidly growing pollen- 



