536 Harris : The fruit of Opumtia 



Opnntia which resemble cladodes, but the other explanation seems 



the more plausible. 



In view of the arguments presented above, the fourth conclu- 

 sion should be modified to read: *'The ovary of Opmitia usually 

 ripens into a fruit-like structure, but it may become modified, as- 

 suming the features of a vegetative stem, persisting as a vegetative 

 part of the plant and producing flowers or vegetative branches, 

 or becoming detached it may serve as an organ of vegetative re- 

 production. In many cases the ovules are few or quite abortive, 

 while the portion of the ovary which maybe described as caulome 

 in nature persists in the form of a vegetative branch." 



In conclusion Professor Tourney remarks : 



I 



* The adverse environmental 



Opuntia 



grows is ample reason for this interesting evolution. The ovary 

 which was once superior has gradually become more and more 



4 



depressed until now it is entirely enclosed in the fleshy branch." 



Ganong * suggests the question as to whether there may be a 

 biological reason for the extremely *' inferior ". nature of the ovary. 



It would be highly interesting if such a character as the inferior 

 or superior nature of the ovary could be accounted for as a result 

 of physical environmental conditions, but unfortunately the evi- 

 dence is entirely inadequate for any such conclusions. Very fre- 

 quently, as a teratological phenomenon and under physiological 

 conditions for the most part but Uttle understood, a primordium 

 which would normally have developed into a sepal or petal or 

 stamen or carpel, gives rise to any one of the others or to a foliar 

 leaf with the peculiarities of the species. It is not at all remark- 

 able, then, that an inferior ovary should sometimes give rise to 

 leaves or lateral appendages or exhibit other peculiarities of the 

 stem. Of this a larger series of illustrations from various forms 

 might be given. The nature of the vegetative shoot in the Cacta- 

 ceae only makes the condition found in the fruit more striking. 



Tme Library, Missouri Botanical Garden. 



* Ganong, W. F. Bot. Gaz. 20 : 213. 1895. 



