170 PROCEEDINGS OF THE ACADEMY OF [1892. 



Both species grow in abundance on my ground and I Lave good 

 opportunity to observe tbeni. B. vulgaris is confined to the low 

 ground and B. prcecox to the high dry ground among cultivated 

 plants. It may be found out of cultivated ground or on waste 

 places of much the same character as on the former, but I have 

 never seen it in the thoroughly native condition of J5. vulgaris. 



B. vulgaris comes into bloom regularly about the first week 

 in May with little regard to whether February or March is 

 fitfally warm, or of a continuously temperate character. B. prcecox, 

 on the other hand, is so easily excited that while in some seasons it 

 will be in flower cotemporaneously with the other species, in others 

 it is nearly over before the B. vulgaris commences to bloom. 

 Habituated to localities favoring such varying conditions of 

 temperature, it Avould certainly acquire the proterandrous character, 

 while the other species under more retardative conditions would 

 become proterogynous. A habit once formed will, we know, con- 

 tinue in plants as well as in animals, by inheritance, long after the 

 causes that induced it have ceased to operate. It is, therefore, quite 

 likely that though B. prcecox were to find itself growing beside 

 B. vulgaris in the low and continuously cool atmosphere of a 

 wet meadow, it would still show for a time much of the proterandrous 

 character it had formed through its earlier associations with other 

 conditions. 



Though I regard environment as having much less to do with the 

 formation of what we must regard as permanent specific characters 

 than is often claimed for it, it is generally conceded to be a great 

 factor in permanent change. The facts here noted certainly indicate 

 its influence in producing dichogamy which would undoubtedly 

 become a fixed character in many instances. 



An extremely interesting point in the close study of the two 

 species is that the proterandrous species is evidently so arranged that 

 cross-fertilization is well nigh impossible. On the other hand the 

 proterogynous species seems incapable of using its own pollen 

 until it has had every chance to receive pollen from other flowers. 

 In the latter case the pistil pushes its way through the unopened 

 perianth, exposing the pin-head form of the capitate stigma. The 

 plants on my ground are in great favor with honey bees, which 

 seem scarcely to care to visit any other flowers Avhen Barbarea 

 vulgaris is abundant, and the exposed stigmas can scarcely avoid 



