INTRODUCTION. 



3 



or the history of the individual organ during its 

 present life-time, once very fashionable, and still 

 very much in vogue because it is usually held that 

 the developmental history of the individual is a 

 recapitulation of that of the race. There can be no 

 doubt that, in a great many cases, this is perfectly 

 true, and that therefore for such cases this method is 

 perfectly reliable ; e. g. in order to determine the 

 nature of the " phyllode "of a mature Acacia-tree, it 

 is sufficient to grow a seedling, when it can be clearly 

 shown from transitional leaf-structures that the 

 " phyllode " is the petiole of the leaf and not the leaf- 

 blade or the entire leaf. On the other hand, it is 

 equally true that the ontogenetic method of research 

 is not always reliable, but just as often, or perhaps 

 more often, yields misleading data, and sometimes 

 even takes a path which is the exact opposite to that 

 of the phylogeny, e. g. the development of an ovule 

 resembles that of a bud more than anything else, and 

 if the ontogeny was our only guide in the matter, we 

 should take it to be a bud, though of a somewhat 

 peculiar type ; but if there is one thing which seems 

 more certain than another, it is that an ovule is not 

 a shoot ; hence, the ontogeny is shown to be absolutely 

 useless for determining its true nature. 



Secondly, there is the anatomical method, upon 

 which various observers, notably Van Tieghem, have 

 resolutely relied in the past. Darwin also made large 

 use of it in determining the structure of orchid-flowers. 

 But it is a mistake to suppose that internal organiza- 

 tion can be relied on by itself for determining the true 

 nature of a doubtful organ ; it is, when the question, is 

 adequately considered, an inverted method of dealing 

 with such problems, and the reverse of this is true; 

 for internal tissues, such as the vascular tissue, will 

 always be laid 'down in accordance with the needs of 

 the organ, and therefore, as a general rule, subsequent 

 in time to its external conformation. As a well-nigh 

 universal rule it may be stated that the anatomical 



