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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