3i6 THE EMBRYO [ch. 



gradually into a terminal bud. How then does this suggestion accord with 

 the demonstration of the primitive spindle, which is the result of comparative 

 study of the earliest embryonic stages not of Ferns only, but also of Algae, 

 of Bryophytes, and of Vascular Plants at large ?(267). 



The two accounts of the embryogeny are entirely out of harmony. The 

 reason for this is that Prof Chauveaud, while stating that his views are based 

 on ontogeny, does not take sufficiently into account the earliest stages of 

 the embryo ; moreover his comparisons are restricted to a limited field. 

 For him the vascular tissue appears to be the criterion of morphological 

 character, and pre-vascular development is not accepted as distinctive {I.e. 

 pp. 75, etc.). But if the ontogeny be traced in each case from the first steps 

 of the embryo, and consecutive stages onward are duly followed, it becomes 

 clear that, however retarded or disguised, the apex of the shoot is defined 

 from the very first. The two views diverge on questions of fact as well as 

 of method : and that here advanced is based on the actual ontogeny as 

 recorded in a very wide literature relating to the embryogeny of plants. It 

 is not a morphology of cell-mosaics, nor of vascular anatomy, but of polarity, 

 which is the feature first to be defined in the individual life. 



There is a certain similarity between the view of Campbell, as stated in 

 relation to Ophioglossuni pedic7iailosuin{2^^), and that of Chauveaud. But 

 the plants which they use as the foundation of their several positions cannot 

 be held as the most primitive even in their own respective alliances. There 

 are good reasons for not holding Ophioglossum as the most primitive genus 

 of the Ophioglossaceae : Ceratopteris and Polypodium, which are used by 

 Chauveaud as illustrations, are both relatively specialised genera of Lepto- 

 sporangiate Ferns. It would appear undesirable to use either of them as a 

 basis for a far-reaching theory of the constitution of the shoot at large. 

 Any such theory should be founded upon a general comparison. When 

 this is done the primitive spindle, and not the " phyllorhize," appears as the 

 original source of the shoot, while the root when present is accessory to it. 

 But, notably, the root is absent from those early leafless vascular plants, 

 the Psilophytales. What then is to be regarded as the " phyllorhize " in 

 these primitive vascular plants which possess neither leaf nor root, though 

 on Chauveaud's hypothesis these should be its essential constituents ? From 

 them we learn that vascular plants antedated the "phyllorhize": and we can 

 only conclude that such a body, even if we concede its apparent existence 

 as a unit in certain instances, is not a fundamental feature for Vascular 

 Plants at larsre. 



