68 ON ALL ORGANIC BEINGS Chap. XT. 



sexes, and must inevitably unite for each birth. With respect 

 to the crossing of hermaphrodites, the subject is too large for 

 the present volume, but in the ' Origin of Species,' I have 

 given a short abstract of the reasons which induce me to 

 believe that all organic beings occasionally cross, though 

 perhaps in some cases only at long intervals of time. 14 I 

 will merely recall the fact that many plants, though herma- 

 phrodite in structure, are unisexual in function ; — such as 

 those called by C. K. Sprengel dichogamous, in which the 

 pollen and stigma of the same flower are matured at different 

 periods ; or those called by me reciprocally dimorphic, in which 

 the flower's own pollen is not fitted to fertilise its own 

 stigma ; or again, the many kinds in which curious mechani- 

 cal contrivances exist, effectually preventing self-fertilisation. 

 There are, however, many hermaphrodite plants which are not 

 in any way specially constructed to favour intercrossing, but 

 which nevertheless commingle almost as freely as animals 

 with separated sexes. This is the case with cabbages, 

 radishes, and onions, as I know from having experimented on 

 them : even the peasants of Liguria say that cabbages must 

 be prevented " from falling in love " with each other. In 

 the orange tribe, Gallesio I5 remarks that the amelioration of 

 the various kinds is checked by their continual and almost 

 regular crossing. So it is with numerous other plants. 



On the other hand, some cultivated plants rarely or never 

 intercross, for instance, the common pea and sweet-pea 

 (Lathyrus odoratus) ; yet their flowers are certainly adapted 

 for cross fertilisation. The varieties of the tomato and 

 aubergine (^Solanum) and the pimenta (Pimenta vulgaris?) 

 are said 16 never to cross, even when growing alongside one 

 another. But it should be observed that these are all exotic 

 plants, and we do not know how they would behave in their 

 native country when visited by the proper insects. With 



14 With respect to plants, an admir- appeared on the same subject, more 



able essay on this subject (Die Gesch- especially by Hermann Miiller and 



lechter-Vertheilung bei den Pflanzen : Delpino. 



1867) has been published by Dr. Hil- 13 'Teoria della Riproduzione Vege- 



debrand, who arrives at the same tal,' 1816, p. 12. 

 general conclusions as I have done. 16 Verlot, ' Des Varietes,' 1865, p. 



Various other treatises have since 72. 



