304 PHILOSOPHICAL NOTES ON* 



Ct 



Fig. laUrt. Vaucheria sessilis (" Pract. Bot.," Stmsb. and Hillh., Fig. 88) 

 (rt, fO are the oil drops, (A, b) antheridium aud oogonium. 



drops of oil are produced by the breaking down of cells, as in the 

 drops of oil which appear m the Citrus oil-gland. 



This, then, to recapitulate, is my view of the oil-glands on the 

 leaves and other parts of the Citrus. They are probably remnants 

 of Fucus or other seaweed conceptacles. Although the fertile 

 conceptacles of this alga are gathered into a head at the end of 

 the branch, nevertheless, the whole frond still remains dotted over 

 with what appear to be atrophied conceptacles, inherited from 

 some previous form like that of Myriodesma, in which the concep- 

 tacles had not yet Ijeen specialized into a reproductive head at the 

 tip of a branch, l)ut were generalized over the frond, that is, every 

 part of the frond bore reproductive organs. These atrophied 

 conceptacles of the Fucus would very probably correspond, as I 

 said, to what are called oil-glands in the Citrus, the latter being 

 the same persistent structures turned to other uses. 



We cannot suppose that in the Citrus the oil-ghmds are of 

 vital importance to th(^ plant, for thousands of other plants have 

 them not, so that it is reasonable to suppose them inherited 

 remnants of some organs that were originally of ^■ital importance 

 to some ancestor. In the Citrus, organs of fructification are no 

 lono-er needed on the fronds proper, because a nuich more 

 specialized organ, in connection with insects and birds, has been 

 developed in the flower and fruit proper. These remnants of 

 ancient reproductive apparatus arc, neverthele.ss, still inherited to 

 point out to us, as it were, the homological history of the tlifferent 

 parts of the higher plants through a long succession of forms 



