n6 SCIENCE PROGRESS. 



for themselves. I do not propose, however, to enter into 

 the earlier history of this matter, as I have already treated 

 of it elsewhere. 1 



Since the introduction by Wolff, R. Brown and Schleiden 

 of embryological study into botany, the conceptions as to 

 the meaning of metamorphosis have become limited to two 

 in number. First, there is the theory of differentiation, 

 and, secondly, that of an actual metamorphosis. According 

 to the first view the embryonic tissue at the growing apex 

 gives rise to indifferent structures which can develop in a 

 variety of ways in accordance with the requirements of the 

 plant as a whole, whilst, according to the latter, a real 

 change takes place of the rudiment (anlage) of one particular 

 organ into another organ, e.g., that of a foliage leaf into 

 a scale leaf, or that of a stamen into a petal. Before 

 inquiring into the grounds on which these rival views 

 are based I shall cite a passage from one of the most 

 recent text-books of botany. Frank/ the author of the 

 work in question, in speaking of the leaf, puts forward the 

 following statement: 3 "When the rudiment {anlage) of a 

 leaf, or leaf segment, which normally would develop into a 

 foliage leaf is compelled in response to other conditions to 

 develop as a scale leaf or as a sporophyll, all that has 

 happened is this, that a leaf rudiment [anlage) may develop 

 into either the one or the other organ ; this, however, is 

 not a real transformation of one organ into another one, 

 for it is always the case that the rudiments (anlage n) which 

 are capable of going through various developments (such 

 as will ultimately result in the production of a foliage leaf, 

 or a scale leaf, or a foliage leaf) are composed of un- 

 differentiated embryonic tissue ; when, however, they have 

 assumed the form of any one of these structures they are 

 incapable of changing into any of the others ". The 

 opinions just quoted are not new ; indeed they represent 



1 Vergleichende Entwicklungsgeschichte d. Pflanzenorgane. Schenk 

 Handbuch d. Botanik, iii., i. 



2 Lehrbuch d. Botanik nach dem gegenwartige stande d. Wissenschaft . 



'■'• Specially directed against my own view of the meaning of meta- 

 morphosis. 



