226 REVIEWS. 



list include sixty-five species, and those in the second sixty 

 species ; the OrchideoB in both being excluded. If the genera 

 in this latter order, as well as in the Asclepiadeaz and Apocy- 

 nacece, had been included, the number of species which are 

 sterile if insects are excluded would have been greatly in- 

 creased ; but the lists are confined to species which were actu- 

 ally experimented upon. The results can be considered as 

 only approximately accurate, for fertility is so variable a 

 character, that each species ought to have been tried many 

 times. The above number of species, namely, 125, is as 

 nothing to the hosts of living plants ; but the mere fact of 

 more than half of them being sterile within the specified 

 degree, when insects are excluded, is a striking one; for 

 whenever pollen has to be carried from the anthers to the 

 stigma in order to insure full fertility, there is at least a good 

 chance of cross-fertilization, I do not, however, believe that 

 if all known plants were tried in the same manner, half would 

 be found to be sterile within the specified limits ; for many 

 flowers were selected for experiment which presented some 

 remarkable structure ; and such flowers often require insect- 

 aid." — (p. 370.) 



It is worth noticing that Trifolium repens and T. pratense 

 (the common "White and Eed Clovers) have a place in the first 

 list; T. arvense and T. procumbens in the second. Darwin 

 refers to Mr. Miner's statement that " in the United States 

 hive-bees never suck the Red Clover," and says it is the same 

 in England, except from the outside through holes bitten by 

 humble-bees ; yet that H. Miiller has seen them visiting this 

 plant in Germany for the sake both of pollen and nectar, 

 which latter they obtained by breaking apart the petals. 

 Darwin has not qualified his statement, long ago made, of the 

 complete sterility of Red Clover protected from insects ; but 

 Mr. Meehan asserts that protected plants are fertile in this 

 country, without, however, giving details or the rate of fertil- 

 ity. In T. arvense, " the excessively small flowers are inces- 

 santly visited by hive and humble-bees ; when insects were 

 excluded the flower-heads seem to produce as many and as 

 fine seeds as the exposed heads." 



