58 OUR NATIVE FERNS AND THEIR ALLIES. 



phase producing spores (sporophyte). The subdivisions of this 

 group are systematically treated in the latter half of this volume. 

 I 35. The Spermaphytes include the highest forms of the 

 plant world. The plant-body (except in rare cases, like Lemna 

 and Podostemon) is a well-developed leafy axis containing highly 

 differentiated tissues. The plant is asexual, producing pollen 

 (microspores) in the authors, and embryo-sacs (macrospores) in 

 the pistils. The sexual or gametophyte stage is greatly reduced, 

 and the process of fertilization of the egg by one of the nuclei 

 of the germinating pollen-grain is too complicated to discuss 

 here. The result of this fertilization is a seed containing an 

 embryo. Three principal groups are recognized : 



1. GymnospermcE (conifers, cycads, etc.). 



2. Monocotyledons (grasses, palms, lilies). 



3. Dicotyiidonce (roses, oaks, maples, asters, etc.). 



1 36. To make the relations of the various groups of pteri- 

 dophytes to each other and to the lower forms of plant life more 

 apparent than can be done in a lineal classification, we present 

 on the next page an outline of a tentative genealogical tree. 



LITERATURE. 



Bower (F. O.). The comparative study of the Meristem of 

 Ferns as a phylogenetic study. In Annals of Botany, in, 305- 

 322, pi. XX-xxiV (1889). 



Is the Eusporangiate or the Leptosporangiate the more 



primitive type in the Ferns ? In Annals of Botany, v, 109-134, 

 pi. VII (1891). 



Campbell (Douglas H.). On the affinities of the Filicinese. 

 In Botanical Gazette, xv, 1-7 (1890). 



A study of the apical growth of the prothallium of Ferns 



with reference to their relationships. In Bulletin of the Torrey 

 Botanical Club, xviii, 73-80 (1891). 



On the relationships of the Archegoniata. In Botanical 



Gazette, XVI, 323-333 (1891). 



