No. 503] NOTES AND LITERATURE 



737 



All leaves, he thinks, are primarily sporophylls. Foliage leaves 

 are reduced sporophylls and cotyledons, and " protophylls" mere 

 modifications of the foliage leaves. This is not, however, a view 

 that can be accepted without some qualification. While un- 

 doubtedly on the theory of antithetic alternation, spore-bearing 

 structures must have preceded foliage leaves, it may be ques- 

 tioned whether these primary spore-bearing structures at least in 

 the case of the Ophioglossacefie and Equisetaceae, were not rather 

 of the nature of sporangiophores than sporophylls in the strict 

 sense of the word. If such is the case, the sterile leaves would 

 be outgrowths of the sporangiophores, or even independent struc- 

 tures rather than direct metamorphoses of sporophylls. 



From a study of the anatomical evidence, the conclusion is 

 reached that the primitive state in the Pteridophytes was one in 

 which the axis was structurally dominant in the shoot, and the 

 type of cauline bundle a solid monostele. It is also concluded 

 that the bipolar, radially symmetrical condition of the sporophyte 

 is more ancient than the dosi-ventral condition. 



The problem of the origin of the roots of the vascular plants by 

 means of which the independence of the sphorophyte is finally 

 secured is recognized as a very difficult one. In some Lycopods 

 no root is formed in the embryo until after several Leaves have 

 been developed, and the name "protocorm" has been proposed 

 for this early undifferentiated plant-body, the assumption being 

 made that it represents an ancient condition antedating a plant- 

 body with true Leaves. Professor Bower, however, is inclined to 

 doubt the accuracy of this hypothesis. 



While recognizing the great value of the evidence of paleophy- 

 tology. and the important contribution that the study of fossils 

 has made to our knowledge of the evolutionary history of the 

 Pteridophytes it is pointed out how very little light has been 

 thrown by this science upon such fundamental questions as the 

 origin of the bryophytic sporogonium or that of the leafy 

 sporophyte. 



In chapter nineteen are discussed the difficulties of determin- 

 ing whether amplification or reduction has been the more im- 

 portant factor in determining the course of evolution in certain 

 cases. Chapter twenty contains a succinct summary of the 

 Working Hypothesis and concludes Part 1. 



Over 400 pages of text with many admirable illustrations are 

 devoted to Part II, "A Detailed Statement of Facts." This is 



