BOTANICAL SUBJECTS. 311 



corals functioning as substitutes of plants. He does not suggest 

 whether these coral plants furnish both food and oxygen to the 

 animals, not improbably they may do both. The carbonate of 

 lime, held in solution by excess of carbonic acid, they withdraw 

 and fix as their solid shell, and the remaining carbonic acid they 

 may somehow decompose to furnish free oxygen for the respira- 

 tion of animals. It is comforting to find that one is not alone in 

 attempting to discuss what might at first sight appear wild 

 aburdities. 



The reader has to run his mind back not to the millipora — that 

 is a side-light — but to the Fuciis, and think of the Citrus leaf and 

 the Fucus frond as cladophyls, having a common ancestry. 



Considering the myriads of modifications through which the 

 leaf has passed, from the Alga frond to the leaf of the highest 

 flowering plants, and the countless forms of leaf now in existence, 

 it is not to be wondered at that comparatively few plants retain 

 traces of the ancestral conceptacles. It is only by putting these 

 remnants to a useful purpose, in connection with insects, that 

 probably they still continue to exist, in an abortive form in the 

 Citrus, the Myrtle, the Eucalyptus, and other plants. 



It would, indeed, be a revolution in botanical thought if some 

 one, some day, were to make it more clear to us that the charming 

 orange tree of to-day was a Fucus in the beginning of time, when 

 vegetation on this earth had not yet emerged from the sea ! 



There are other plants besides those with oil-glands which 

 give indication of having remnants of what I think are ancient 

 conceptacles. Many of the Crassulace^e have little ring-dots on 

 either the upper side only or on both sides of the thick leaf. In 

 some these dots are indentations, which to my mind would 

 indicate that originally they were little reproductive cavities. I 

 have not seen the origin of these Crassula dots noticed anj'where. 



Crassula aborescens (Wild.) has them very plainly. Where the 

 leaf is thin these dots can be seen, by transparency, as little clear 

 circles. 



Figs. 



The fruit we call fig is considered by botanists as a receptacle 

 similar to those of the Compositae ; that is, the expanded end of a 

 branch studded with sessile florets. The fig, however, is a closed 



