230 REVIEWS. 



uous flowers are visited much more frequently and by many 

 more kinds of insects than are small inconspicuous flowers. 

 He further remarks that the flowers which are rarely visited 

 must be capable of self-fertilization, otherwise they would 

 quickly become extinct." Mr. Darwin's list seems to show 

 that, as a rule, they are so ; yet many very small flowers, like 

 those of Trifolium arvense, and small and dingy ones, like 

 those of Asparagus, are freely visited by bees ; and, con- 

 versely, many large and conspicuous flowers which are fre- 

 quented by insects are none the less self-fertilizable. Through- 

 out we find that such things do not conform to arbitrary or 

 fixed rules ; and this favors the idea that the differences have 

 been acquired. Mr. Darwin conjectures that the self-fertiliz- 

 ing capabilities of many small and inconspicuous flowers may 

 be comparatively recent acquisitions, on the ground that, if 

 they were not occasionally intercrossed, and did not profit 

 by the process, all their flowers would have become cleisto- 

 genous, " as they would thus have been largely benefited by 

 having to produce only a small quantity of safely protected 

 pollen." 



Mr. Darwin's experiments tending to prove that cross-fer- 

 tilization between flowers on the same plant is of little or no 

 use, he is naturally led to consider the means which favor or 

 ensure their fertilization with pollen from a distinct plant. 

 This must needs take place with dioecious plants, and is likely 

 to occur with the monoecious, and is in some cases secured (as 

 in "Walnut and Hazelnut) by some trees being proterandrous 

 and others proterogynous, so that they will reciprocally fer- 

 tilize each other. In ordinary hermaphrodite species the ex- 

 pansion of only a few blossoms at a time greatly favors the 

 intercrossing of distinct individuals, although in the case of 

 small flowers it is attended with the disadvantage of render- 

 ing the plants less conspicuous to insects. Our common 

 Sundews furnish a good illustration of this. They abound 

 wherever they occur, and are for a long while in blossom, 

 but each plant or spike opens but one flower at a time. The 

 fact of bees visiting the flowers of the same species as long as 

 they can, instead of promiscuously feeding from the various 



