THE TAXONOMY OF PHANEROGAMS 165 



regard unisexuality as a criterion of more than subordinate 

 importance. 



As the Genera Plantarum appeared at intervals between 

 1863 and 1880 it must seem somewhat remarkable to you 

 that there is not the slightest expression in the work of 

 the evolutionary ideas that were then influencing so 

 profoundly all other branches of the science, and notably 

 the taxonomy of the Cryptogams, which Bentham and 

 Hooker did not touch. But Bentham was a firm believer 

 in the dogma of the constancy of species, and he explains 

 his position in the following words : "I can scarcely 

 think that due allowance is made for those who hke 

 myself through a long course of study of the phenomena 

 of organic Hfe had been led more and more to believe in 

 the immutability of species within certain limits, and have 

 now felt their theories rudely shaken by the new hght 

 opened on the field by Mr. Darwin, but who cannot 

 surrender at discretion so long as many important outworks 

 remain contestable." This is Bentham's Apologia in 

 1863, but ten years afterwards he felt himself driven to 

 accept the new doctrin'e, too late, however, to make 

 feasible any attempt at modifying the plan of the Genera. 

 Probably his fellow worker. Hooker, who was a consistent 

 supporter of Darwin, had no small share in bringing about 

 the conversion of the veteran systematist to the new 

 views. 



I must not omit to remind you that it is to Bentham 

 that you owe the Handbook of the British Flora whose aid 

 you are accustomed to seek on all your field excursions, 

 a book, by the way, with the writing of which Bentham 

 is said to have " amused himself before breakfast " ! 



The other attempts at classification that were made 

 during the concluding years of the nineteenth century 

 need not detain us long. 



The discovery by Treub in 1891 that in the Australian 

 genus Casuarina the pollen tube enters the ovule by the 

 chalaza and not by the micropyle in the usual way led 



