264 



The Plant World. 



Again, a mass of pollen was placed near the apex of the lower lip, 

 either transversely or obliquely (Figure 6, b). In nearlv every 

 instance in twenty-four hours there was a marked curvature in 

 the tissue beneath the pollen (Figure S), but not elsewhere, the 

 lips remaining distinctly open except when withering began. In 

 a few exceptional cases, the failure to curve may be due to the 

 condition or character of the pollen, though I found no evidence 

 of differences such as are observed by Burck in Torenia but not 

 in Mimulus with which latter Diplacus has agreement therefor 

 in this regard. 



Fig. 1. 



The conclusion appears therefore to be justified that the 

 curvatures observed in the stigma-lips after the application of 

 pollen are due entirely to the withdrawal of water from the un- 

 derlving tissues, either before or during the germination of the 

 pollen, but between these I have made no effort to decide. The 

 potent factor in bringing the Ups into their final position is, I 

 believe, the mechanical quality of the coUenchyma-like outer 

 epidermis. Mv observations therefore substantiate the con- 

 clusions of Burck on Mimulus, except that in Diplacus the 

 stigma lips open after pollination and close only after the lapse 

 of some time, beginning in about three hours. An inquirv into 

 the character of the pollen in these plants and into its behavior 

 toward the stigma might very well elucidate this difference. 



Heat. In order to avoid the drastic effect of dr\' heat, 

 which causes withering, I used a tubulatured bell jar standing 



