160 DICHOGAMY, ETC. [CH. 



It is clear that in these cases the flower is susceptible 

 at least to an occasional cross, but at the same time 

 assured of good chances of self-pollination if no cross 

 occurs. 



The student will also understand that every gradation 

 between complete and incomplete Dichogamy and Auto- 

 gamy occur, and that the only philosophical explanation 

 of the prevalence of the former is that some advantage to 

 the plant is ensured, as follows from Darwin's prolonged 

 investigation of the subject. 



Just as incomplete Dichogamy is comprehensible when 

 we understand the significance of Dichogamy generally, 

 so, too, is a second derived condition of affairs where 

 although both androecium and gynoecium exist in the 

 same flower, one or other is so delayed in its development 

 that either no pollen is produced or no ovules are formed, 

 and so the flower though morphologically hermaphrodite 

 (monoclinous) is physiologically unisexual (diclinous). All 

 gradations of this pseudo-hermaphroditism occur, by 

 abortion of all the stamens, or of some only, or by the 

 pollen being incapable of germination ; by abortion of 

 the whole ovary, or of the ovules, or by the stigma 

 shrivelling up and being non-receptive, and so on. 



Excellent examples of the various cases are furnished 

 by the following native plants: (1) Polygonum Bistorta, 

 Galium Gruciatum, Anthriscus, Caucalis, Sanicula, &c., 

 where apparently hermaphrodite flowers with abortive 

 pistils (pseudo-hermaphrodite male) occur among the com- 

 plete ones; (2) Petasites, Tussilago, &c., where pseudo- 

 hermaphrodite male flowers are mingled with pistillate 

 flowers. (3) In the Sycamore and Norway Maple, Bay 

 Laurel, Rumex obtusifolius and other Docks, Pellitory, &c., 

 we find the polygamous flowers comprise mixed herma- 

 phrodite and pseudo-hermaphrodite male (with rudimentary 



