IN ANIMALS AND IN PLANTS 175 



geny of any higher sporophyte is- a much less essential incident in the 

 whole development than that in any higher animal : the embryogeny of 

 a higher animal is at best only comparable with the initial embryogeny 

 of a plant where the embryo is still enclosed in the tissue of the parent : 

 it has' no counterpart corresponding to that continued embryology which is 

 so long maintained in the apical region of the plant-body. 



Secondly, the sporophyte is now believed to be itself an intercalated 

 phase, which has assumed increasing proportions in the course of descent, 

 while the function of spore-formation, which comparison tells us was the 

 initial function of the sporophyte, has been proportionally delayed. If 

 this be true, so far from the first formed parts being in their present 

 form the prototypes, they would be more correctly recognised as derivatives,, 

 modified, or it may be transformed, during later evolutionary periods. 



The absence of strict analogy between the embryogeny of the higher 

 animals and the higher plants is further illustrated in relation to the theory 

 of germinal layers. Following on the experience of animal embryologists 

 who found that definite regions of tissue of the mature animal body are 

 referable in origin to definite germinal layers of the embryo, Famintzin 

 undertook to prove that the same holds for the definite systems of 

 epidermis and vascular tissue in the Angiosperms. It is true that the 

 origin of the epidermis and of the central stele gives some countenance 

 to such a view, though even in these it is not difficult to quote exceptions 

 where that regular mode of origin does not exactly apply. But the 

 question becomes critical with regard to those parts of the vascular system 

 which pass from the stem into the leaves : do these originate from the 

 plerome system of the axis, as by the theory of germinal layers they ought 

 to do? As De Bary pointed out, 1 this could not be otherwise effected 

 than by outgrowths of the plerome pushing between the other layers of 

 the young forming leaf. But as a matter of fact, they are derived from 

 the primary periblem, and definite bands of this tissue show the corre- 

 sponding differentiation, by which means the vascular system of the leaf is 

 connected with that of the axis. This almost forgotten discussion is quoted 

 here as an example of an attempt, actually made, to impose an embryo- 

 logical idea derived from the study of animals upon the embryology of the 

 higher plants ; and it shows how, when submitted to the test of detailed 

 observation, it has been rejected. It must be clearly understood that such 

 comparisons deal only with distant analogies, and that for reasons such as 

 those already explained the methods and arguments of animal embryologists 

 are not transferable to the embryology of the sporophyte of plants. In 

 point of fact, hitherto plant-embryology owes little to animal embryology 

 beyond the confusion of thought which follows on fallacious comparisons. 



The success of Naegeli and Leitgeb in recognising and delineating the 

 apical cell, and the regular succession of its segmentations in various 

 plants, turned the course of accurate observation about the middle of 

 1 Conip. Anaf. Engl. Eel., p. 23. 



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