736 



THE AMERICAN NATURALIST 



[Vol. XLII 



specialized leptosporangiate ferns can be clearly followed in 

 existing types. Professor Bower does not regard the Ophio- 

 glossales as related to the true ferns, but from this view we feel 

 obliged to dissent. 



As might be expected, much stress is laid upon the "Theory of 

 the strobilus" with which Bower's name is especially associated. 

 This theory assumes that from some hryophyt ie sporangium, 

 perhaps not very different from that of Anthoceros, by the 

 segregation of definite sporangia each subtended by a leaf-like 

 organ originating from the sterile tissue between the sporangia, 

 a cone or strobilus would be derived, i. c, an axis upon which are 

 borne a number of leaves usually spirally arranged, each one sub- 

 tending a sporangium. This condition is still met with in some 

 of the simple species of Lycopodium like L. selago and it is an 

 extremely ancient one. 



This theory of the strobilus when applied to the Lycopods has 

 very much in its favor, and is certainly the most plausible ex- 

 planation yet put forward as to the origin of the Lycopods; but 



reason to suppose that it is a secondary condition. 



The chapter on "Embryology and the Theory of Recapitula- 

 tion" is a very sane treatment of an extremely difficult problem. 

 While recognizing that the first students of vegetable morphol- 

 ogy went much too far in their insistence upon the importance of 

 the exact succession of cell divisions in the young embryo in their 

 relation to the subsequent organs of the plant, nevertheless it is 

 unquestionable that the early divisions of the embryo are to a cer- 

 tain extent a recapitulation of the early phylogeny. It must be 

 remembered that the young embryo has been subjected for 



these conditions certain definite early segmentations should be 

 fixed i s merely what would be expected. One of these conditions 

 is the action of gravity and this beyond question is the most im- 

 poi" taut I act or in determining the marked polarity of the embryo. 

 As to the general application of the theory of recapitulation to 

 the Later stages of development, as Professor Bower very well 

 points out. great caution has to be used, but nevertheless within 

 proper limits it is justified. 

 Professor Bower maintains that there is but one type of leaf. 



