﻿ADAMS— POLLEN GRAINS 



In my experiments, on the other hand, I found that absence of 

 oxygen prevented the germination of the pollen grains. Miyoshi 

 (i) found that cane sugar, grape sugar, and dextrin exerted espe- 

 cially strong chemotropic attraction on pollen tabes, and that the 

 first penetration of the stigma by the pollen tube was induced by 

 chemotropic stimulation aided by the hydrotropism of the pollen 

 tube, and possibly also by aerotropic and other stimuli. 



Sandsten (3) carried out an extensive series of experiments 

 with pollen grains. He found starch, diastase, and invertase in 

 all the pollen grains which he examined. He also found diastase 

 and invertase in the tissues of the style and stigma. He used 

 hanging drop cultures of saccharose in almost every case. For 

 the species of plants that he experimented with he found the 

 optimum strength of sugar solution to lie between 5 and 35 per 

 cent, but 20 per cent was the rule in the majority of instances. He 

 found the range of concentration of the cane sugar for any given 

 species of pollen to be large, indicating differences of degree of the 

 concentration of the juices of the stigma. For instance, pollen of 

 Narcissus Tazetta germinated in 1 per cent solution of cane sugar 

 and also in a 60 per cent solution. He says that bursting of pollen 

 takes place in masses of apple and plum pollen during warm spring 

 rains, while in distilled water the contents protruded a distance 

 equal to the diameter of the pollen grain, but made no further 

 growth. I found a somewhat similar protrusion of contents in 

 some of the sugar solutions used, but should hesitate to regard this 

 as true germination. Sandsten further states that most pollen 

 grains are negatively aerotropic and chemotropic, and that the 

 direction of growth of the pollen tube is away from the light. 

 Elsewhere he states that sunshine had little or no effect on the 

 germination of the pollen or upon the growth of the pollen tube in 

 most plants. In my experiments I found no difference in germi- 

 nation in the case of pollen grains kept in total darkness as com- 

 pared with others exposed alternately to darkness and light. 



Regarding the relation of the pollen grains to temperature, the 

 temperature of the laboratory in Sandsten's experiments varied 

 from 15 to 36 0 C. He found the optimum degree of temperature 

 for the germination of apple, pear, and plum pollen to be 24 0 C. 



