174 THEORY OF RECAPITULATION 



observations, which were thus initiated among the lower Cryptogams, to 

 the Archegoniatae and the Phanerogams, he secured that morphological 

 ideas, hitherto drawn primarily from the Phanerogams, should be examined 

 in the light afforded by the history of development in the Cryptogams. 

 And thus the way was prepared for the brilliant embryological work of 

 Hofmeister, who, after investigating the embryogeny of the Phanerogams, 

 tracing the individual from the egg onwards, proceeded to apply the 

 same method to the Bryophytes and Pteridophytes, with the results 

 which are now permanently interwoven into the web of the science. It 

 may be said that subsequent work in this direction has done little more 

 than to fill in the details in the areas of observation left blank upon the 

 morphological map thus plotted in broad outline about the middle of the 

 last century. It is in the interpretation of the facts, and the recognition 

 of the evolutionary history which they convey that there has been room 

 for some difference of opinion : and it is this that will now be discussed. 



While the elucidation of the facts by Naegeli, Hofmeister, and others 

 was proceeding, the belief in the mutability of species became prevalent : 

 the Darwinian theory seemed, as we have already seen, to provide a natural 

 explanatory thread running through the facts of genetic morphology and 

 connecting them into an evolutionary history. It was held that the 

 successive events of the individual life directly illustrated the course of 

 descent ; as regards the sporophyte the first stages were accordingly 

 regarded as phylogenetically the earliest, and consequently for comparative 

 purposes the most important. Embryological detail was thus given a high 

 place in comparative morphology. Analogy with the results and arguments 

 of zoologists seemed to support this position, and just as some consistent 

 reflection of the phylogenetic history was found in the beginnings of the 

 individual life of the higher animals, so, it was held, should be the case 

 with the plant : the embryology of the sporophyte was accordingly made 

 the basis of a consecutive history of its development in the race. For 

 instance, the first formed leaves were held to represent the primitive and 

 original foliar type, and those formed later on in the individual life were 

 regarded as subsequent in the history of the race : or, carrying this lin< 

 of thought further into detail, the order and position of the first segmenta- 

 tions in the ovum were regarded as of special comparative importance, and 

 were used as the basis of elaborate theorising. 



But before such conclusions are accepted, it is well to reflect upon 

 the profound differences which exist between the embryology of the higher 

 animals and that of the sporophyte in plants. In the first place, the 

 embryogeny of the higher animal is carried out once for all after fertilisa- 

 tion : the main parts are laid down at a comparatively early stage, and are 

 not repeated later. But in the sporophyte of all Vascular Plants the 

 initial embryogeny is merely a preliminary phase leading to that continued 

 embryogeny which involves the repeated formation of parts : this is main- 

 tained throughout the active life of the plant. Hence the initial embryo- 



