CHAPTER XXVII 



SEED-BEARING PLANTS (Continued) 



LIFE HISTORY OF AN ANGIOSPERM 



386. Variations in Life Histories. In the groups pre- 

 viously studied there is a marked uniformity or similarity 

 in the life histories, making it comparatively simple, once 

 one has the key, to interpret the structures involved. 

 Even as we pass from one group to the next, homologies 

 are detected without serious difficulty. Under various 

 more or less transparent disguises, we have been able to 

 trace such structures as the sporophyll, spore-case, 

 microspore and male gametophyte, megaspore and female 

 gametophyte, and, in the latter, the archegonium, egg, and 

 embryo. But studies of the highest group of plants, the 

 Angiosperms, soon lead us into difficulties not readily 

 overcome. It is not difficult to detect the sporophylls, 

 spore-cases, megaspores and microspores; but, just as 

 among the Gymnosperms the antheridium had dis- 

 appeared as a distinct, fully developed organ, so among 

 the Angiosperms the archegonium has disappeared, and 

 certain new structures have made their appearance. Thus 

 it is not possible to choose from the Angiosperms any 

 actual plant whose life history, in detail, is typical of the 

 entire group. For external features any one of several 

 plants might be chosen to illustrate the floral organs 

 commonly met with. The life history of the yellow 



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