182 EVOLUTION OF PLANTS 



Angiosperms, but shall refer to this later. The effect 

 of fertilization may extend beyond the fruit itself and 

 involve the calyx, as in the apple or pear, or even the 

 summit of the floral axis, as in the strawberry or fig. 



The embryo-sporophyte in different Angiosperms 

 shows a very different degree of development at the 

 time the seed ripens. Sometimes, especially in para- 

 sitic plants, it consists merely of a small mass of cells 

 without any external differentiation. On the other 

 hand, as in the pea family, it finally occupies the whole 

 cavity of the seed, and all the parts, stem, root, and 

 cotyledons, and the terminal bud, are perfectly formed. 



The remarkable complexity shown by the fully devel- 

 oped sporophyte of the Angiosperms offers a marked 

 contrast to the extremely reduced gametophyte, and it 

 is in this group that the development of the sporophyte 

 reaches its most complete expression. From minute 

 undifferentiated aquatics like the little duckweed 

 (Lemna) (Fig. 45, D), every grade of development is 

 encountered, up to trees rivalling the giants among the 

 Conifers in point of size, and far surpassing them in the 

 perfection of their parts, especially the flowers. 



In marked contrast to the Gymnosperms, which are 

 restricted in their range, some forms of Angiosperms oc- 

 cur under all conditions. Some are aquatics, even grow- 

 ing in the ocean, while others are inhabitants of almost 

 absolute deserts. Some are stately trees, while others 

 are minute, almost microscopic, herbs living but a few 

 weeks. Especially in the tropics, where the struggle 

 for existence is keen, do we find Angiosperms taking 

 advantage of every opportunity offered, some lift 

 themselves by tendrils or by twining their stems about 



