168 COMPENDIUM OF GENERAL BOTANY. 



equal morphological value is subsequently followed by a physio- 

 logical dissimilarity. Occurrences in the vegetable kingdoms teach 

 us that, for example, not all tendrils and thorny structures originate 

 in like manner, that is, from rudiments known as foliar protuber- 

 ances (tendrils of Lathyrus and spines of Berberis] ; some originate 

 in the manner of branches (the tendrils of the grape, the thorns of 

 Rhamnus cathartica). The conceptions " thorn " and " tendril " 

 are therefore physiological, and not morphological. The second 

 feature of metamorphosis is that morphologically unequal organs 

 may be equal in value physiologically. Of this occurrence physio- 

 logical anatomy knows so many examples that the entire phenome- 

 non has come to be looked upon as a law of nature. The foregoing 

 has shown us what metamorphosis in the botanical sense means. 

 It is hoped that it has also made clear that it does not mean the 

 transformation of one organ into another? 



There is still another interesting condition to be mentioned : 

 the correlation of the growth of organs. This is readily understood 

 from the standpoint of teleology. One example will suffice to 

 illustrate what is meant. If one cuts away the young shoots of a 

 potato-plant, new lateral shoots will be formed which would other- 

 wise have developed into tubers ; that is, organs which were 

 originally intended to remain underground and form storage-tissue 

 for reserve material under certain conditions will form aerial organs 

 developing green leaves having the function of assimilation. This 

 phenomenon can readily be explained from the standpoint of 

 physiology, but cannot be rationally explained from the causal- 

 mechanics of organ-development, as SACHS is inclined to believe 

 (see ref., p. 167). 



II. OBIGIN AND POSITION OF LATEKAL ORGANS, 



AND THE CAUSES FOE THEIR DEFINITIVE 



POSITION. 



How is a system of organs formed? or, more specifically, how 

 and when do new organs develop from those already existing? 

 Upon what is the final position of the organ dependent ? 



These are the questions which shall interest us now. As is in- 

 dicated, there is a difference in the origin of organs as well as in 



1 GOBEL'S metamorphosis of organs I have discussed elsewhere; also the sub- 

 ject of "correlation " as opposed to the views of SACHS (see citation above). 



