MORPHOLOGY OF AXGIOSPERMS 



wer-e ^presented separately because of the diversities; 

 e morphological diversities among Angiosperms seem to 

 be not so much those of groups as of habit and habitat. While 

 it is generally agreed that the seed-bearing habit was devel- 

 oped independently in more than one phylum, and that the 

 Gymnosperms and Angiosperms have probably no immediate 

 phylogenetic relation to one another, it is of interest to note 

 the essential contrasting features of the two great seed-bearing 

 groups. 



The chief contrast in the sporophyte is that in Gymno- 

 sperms pollination results in bringing the pollen in contact 

 with the ovule, while in Angiosperms the result of pollination 

 places the pollen in contact with a receptive surface developed 

 by the carpel. This contrast involves great differences in mor- 

 phological structure, so great, in fact, that it is hard to imagine 

 one of these conditions as having been derived from the other. 

 The method of pollination might also be mentioned as a con- 

 trasting feature, since the primitive anemophilous habit seems 

 to be universal among the Gymnosperms, while among Angio- 

 sperms it prevails only among those groups that may be re- 

 garded as primitive. There accompanies this contrast a similar 

 one in connection with the flower. Just how this structure 

 may be defined is considered in the next chapter, but the char- 

 acteristic flowers of Angiosperms have no representative among 

 Gymnosperms, however much the older morphology felt com- 

 pelled to homologize them. However, the method of pollination 

 and the flower are but corollaries to the fundamental contrast 

 involved in the contact of the pollen with the ovule in the one 

 case, and with the carpel in the other. 



A second fundamental distinction in connection with the 

 sporophyte is to be found in the embryogeny of the two groups. 

 In the Gymnosperms, the free nuclear division within the fer- 

 tilized egg, and the use of the bulk of the egg as a food re- 

 serve in most forms are in sharp contrast with the absence of 

 free nuclear division in the Angiosperm egg, a character ap- 

 pearing, however, in Gnetum and Tumboa. 



If the contrast between the sporophytes of Gymnosperms 

 and Angiosperms be pressed into anatomical details, the differ- 

 ences are found to be quite as striking, though perhaps a little 

 more perplexing. 



