86 MAINE AGRICULTURAL EXPERIMENT STATION. 1904. 



decaying in from three to five days after pollination. Again with 

 Oncidium Hexuosum, the plant's own pollen and that of a dis- 

 tinct species were placed side by side, and after five days the lat- 

 ter was perfectly fresh, while the plant's own pollen was brown. 

 These observations are remarkable, for they show that the plant's 

 own pollen not only fails to impregnate the flower, but acts on 

 the stigma, and is acted on in an injurious or poisonous manner. 

 Such action seems to be mutually poisonous. 



In 1897 Gould 1 confirmed the work of the older investigators. 

 At the conclusion of his thesis he says : "The power of pollen to 

 produce fecundation exists in every possible degree from perfect 

 potency to absolute impotency. Pollen, like seeds, may be so 

 low in degree of vitality as to be unable to germinate, or be so 

 retarded in its germination that the elements do not come 

 together till the period of receptivity is past. External condi- 

 tions such as temperature and moisture may influence the vitality 

 of pollen and its potency." 



Some recent work by Booth 2 concerning the self-sterility of 

 grapes throws further light on the inactivity of pollen. Results 

 of experiments carried on for several years are summarized in 

 this manner : Poor pollen may be known by a microscopical study 

 of the structure of the grains ; the infertile grains are irregular 

 in shape and have sharp angles, — also by the arrangement of 

 pollen, either dry or in fluid media. Fertile pollen comes 

 together in clusters by means of its mucilaginous coatings. 

 Sterile pollen does not have this coating, and comes together only 

 by chance. Culture experiments showed the self-sterile pollen to 

 be lacking in viability, for in most cases such pollen either failed 

 to germinate or gave a low percentage of germination. Such 

 pollen was impotent on pistils of self-sterile varieties, as well as 

 on its own stigmas. Booth explains the reason for this condition 

 of things, as a probable indication that the flowers of the grape 

 are in an evolutionary stage, and are passing from hermaphro- 

 dite to staminate and pistillate forms. Mention of these cases is 

 made here to show how infertility is expressed, for the problem 

 of impossible reciprocates bears hard on the subject of sterilty. 



(2.) Lack of nourishment of pollen tubes. 



1. H. P. Gould, Potency of Pollen, Cornell University Thesis, 1897. 



2.. N. O. Booth, N. Y. Agr. Exp. Sta. Bui. 224. A Study of tirape Pollen 



