PARTIAL DICLINISM. 225 



intimate connection between the corolla and androecium, and 

 thinks that " the decreased size of the female corollas is due 

 to a tendency to abortion spreading from the stamens to the 

 petals." 



In noting all the plants mentioned by Miiller and Mr. 

 Darwin as gynodioecious, there are besides the two well- 

 marked groups already mentioned, viz., Alsinece and Labiatce, 

 the following isolated genera or species, Pelargonium, Gera- 

 nium macrorhizon, Sherardia arvensis, Valeriana montana, 

 Scabiosa, Cnictis, Echium vulgare and Plantago ; to the 

 Compositce, I can add Achillcea millefolium; and I think 

 also Vines may be included in the list. 



The first and important point to note about the flowering 

 of the Alsinem is that the female flowers are the first to open, 

 at the beginning of the season* It is the same with Geranium 

 macrohizon. Pelargonium, and Cofiee in Guatemala. Now, 

 we have already seen how sensitive the androecium and the 

 corolla are to a low temperature, so that we have here a direct 

 cause •which will account for the check upon the growth and 

 development of these two whorls. Applying this principle 

 to the Labiates, we must remember that as a group they are 

 correlated to a warmer climate, their " home " being the 

 Mediterranean and even warmer regions ; hence I assume 

 their greater hereditary sensitiveness to a low temperature 

 in those descendants which occupy a cooler temperate zone. 

 This may, I think, account for the predominance of purely 

 female forms, as well as the presence of stamens in every 

 degree of degeneracy. 



How far the same principle will apply to the other 

 gynodioecious genera and species, I will not pretend to 

 offer an opinion, as not enough is yet known about them ; 



* See Hildebrand's observation, p. 234, and SEiUALlTir and Tempeea- 

 TUEE, p. 237. 



