438 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



products of Styles and of ovules in forms fully self- and cross-fertile 

 is fully indicative that a decided retinement of method is neces- 

 sary to determine the conditions operating in such fluctuating 

 cases of fertility as are seen in self- and cross-incompatibilities. 



It has, however, been quite generally shown, in agreement with 

 Jost's ('07) results, that in self-sterility from physiological incom- 

 patibility the tubes grow more slowly and do not penetrate to 

 the ovary in the time required for fertilization. This has been 

 taken as evidence of the inhibitory action of specific stuffs (indi- 

 vidual stuffs of Jost, line stuffs of Correns) or of the lack of proper 

 nutritive substances (Compton '13; East 'ISa). Certain phases 

 in the determination of this point admit of experimental proof 

 and the writer is planning experiments in this particular. If 

 pollen tubes admitted of ready growth in cultures, extracts of 

 inhibitory or stimulating substances might be made and their 

 action determined. Thus far, however, no essential differences 

 have been found in the physiology of the pollen of self-fertile and 

 self-sterile plants of the same species. It would seem that some 

 such differences must exist comparable to the marked differences 

 in the growth of pollen tubes in the ineffective and the effective 

 pollinations. The difficulty of securing any sort of germi-nation 

 in chicory seems to prohibit this sort of study in this plant. 



Some misunderstanding appears to have arisen in regard to the 

 results of certain investigators. Jost's determination that a par- 

 ticular structure of the ei:)idermis prohibits germination of pollen 

 in Corydalis cava gi\es no clue to the causes of self-sterility in this 

 species, as such a condition prohibits the germination of all pollen. 

 After the epidermis is broken the plant's own pollen will germinate 

 as will the pollen of other plants, but its growth is more feeble. 

 The cause of self-sterility is here not concerned with the germina- 

 tion of the pollen. Likewise in Cytisus Laburjiiim the term self- 

 sterility is used l)y Jost, inad\ isedly, for here the structure of the 

 ej^idermis seems to make the injury of stigmas necessary for the 

 growth of any pollen and hence it is not self-sterility but complete 

 sterility that is conditioned by an unbroken epidermal surface. 

 These are interesting cases of \ery special adaptations that favor 

 cross-fertilization. 



Martin ('13) has (hawii the high!}- suggesti\'e conclusion that 

 in red cioNer the necessity for a delicate regulation of water supj)ly 



