CRYPTOGAMS AND PHENOGAMS 557 



gametophyte, while the other is the essential part of a gamete. Here 

 then is a gametophyte reduced to the simplest terms. The female 

 gametophyte formed within the embryo-sac consists of a few cells 

 forming two groups which lie at opposite ends of the macrospore. 

 Those at the micropylar end (ci) include an egg-cell which is thus 

 advantageousl.y situated for fertilization by the pollen-tube entering 

 the micropyle. The growth of the embryo from the fertilized egg- 

 cell involves, as shown in Fig. 383, the formation of a suspensor (et) 

 which pushes the developing germ well into the mass of food. In 

 this example the embryo comes to fill the sporangium completely 

 while still attached to the parent, thus forming an exalbuminous 

 seed, in which radicle, cauliclc, and cotyledons are well developed. 



While it is not altogether clear how closed ovaries evolved 

 from open carpels, the change may well have taken place 

 as a result of the peculiar inrolling of the young leaf-lobes 

 which primitive gymnosperms are supposed to have inherited 

 from ferns. If ovules should form on such lobes while still 

 inrolled, and the lobes should coalesce, the carpel would be 

 angiospermic. However it happened, many highly important 

 consequences of this advance are apparent. Most obvious 

 is the greater protection of the offspring during the period of 

 their dependence. 



There is also an enormous gain in possibilities for securing an 

 advantageous cross. Thus a moist, projecting stigma becomes a 

 target more likely to be hit by wind-carried pollen grains and more 

 likely to insure their prompt germination, than the micropj^le of 

 a naked ovule. Expansion or branching of the stigma, such as 

 we find to be characteristic of wind-pollinated angiosperms, shows 

 how well this new organ lends itself to increasing the chances of 

 pollination and at the same time favors economy in the amount 

 of pollen produced. See Figs. 2-15, 27, 36, 74 B, C, 109 C, D, 124 

 B, 153, 159, 165 //, 171 //, 243, 248, 254, 256 B, 257, 267 D, etc. 

 A still further advance in these directions came when insects and 

 other animals were attracted to the flowers, and their services thus 

 secured as carriers of pollen. The attractive odors, bright colors, 

 and alluring sweets, together with the marvelous arrangements of 

 the various floral organs, present modifications of endless variety 

 and offer one of the most fascinating fields in the whole range of 

 botanical studv. See Figs. 22, 39 //, 48, 57, 59 77, SO, 91-100, 106, 

 133, 139, 145, 148, 156, 163, 164, 168 //, 172, 178, 187, 188, 189, 192, 

 217, 251, 275, 276, 282-293, 299, etc. 



This elaborate modification of stem-parts and leaf-parts cooperat- 

 ing with pollen-sacs and ovules to form what we call a flower brings 

 with it the further possibility of utihzing these accessory organs, 



