INTRODUCTION. 11 



spermatozoids, the male gametes, which fertilize other 

 specially differentiated cells, the oospheres or female 

 gametes. The oospore, which results from this fertiliza- 

 tion, develops into the sporophyte or ordinary Fern plant. 

 /The differentiation into root, stem, and leaf is well 

 marked, as is also the development of fibrovascular 

 bundles. 



The Spermaphytes. Here also the ordinary form of the 

 plant is the sporophyte. Two kinds of spores are borne, 

 microspores or pollen grains, and macrospores or embryo sacs. 

 Each kind of spore develops into a minute prothallium, 

 and these prothallia represent the gametophyte. The 

 male gamete is either the original nucleated protoplasm 

 of the pollen grain, or is one of the nucleated cells formed 

 by the division of that protoplasm in the formation of the 

 male prothallium in a tube which grows out of the pollen 

 grain. The female gamete is a nucleated cell situated 

 near one end of the female prothallium, which is formed 

 in the embryo sac in the ovary of the pistillate flower. 

 From the fertilization of the female gamete by the male 

 gamete there results a seed which distinguishes this 

 group from the three lower groups. The differentiation 

 into root, stem, and leaf, and the development of the 

 fibrovascular bundles reach their perfection in the Sper- 

 maphytes. 1 



Beyond this grouping of all plants into Thallophytes, 



1 It is not expected that the beginner will gain very definite ideas of 

 the facts which have determined these four great groups from reading 

 the preceding paragraphs. A clear conception of these facts will come 

 only after the actual observation and study of plants which show these 

 distinguishing characteristics. Attention will frequently be called to 

 these points in connection with the practical studies of plants in the fol- 

 lowing pages. Whenever attention is thus directed to the principles 

 which have led to the separation of all plants into these four groups, the 

 pupil should read and reread these paragraphs until he gains a clear con- 

 ception of the principles. 



