1889.] NATURAL SCIENCES OF PHILADELPHIA. 61 



pollen, notwithstanding its sub-gelatinous character, might not be 

 carried by the wind. 



It was subsequently made clear that the pistils did not emerge 

 from the floral envelopes till after fertilization had been accomplished. 

 Indeed the seed had advanced considerably towards maturity before 

 the styles were projected. It was only by the increased growth of 

 the achenium following fertilization that the styles became exposed 

 at all. The flowers are fertilized in the bud ; there is no possibility 

 of cross-fertilization. It may be remarked here, that the word 

 " cross-fertilization" is used to express the pollination of a flower by 

 another on the same plant. The physiological speculations involv- 

 ing questions of benefit to the plant or to the race, require the cross 

 to be between different plants growing under separate conditions. 



It was but natural to examine other Polygoni, in the light of the 

 facts developed by P. Virginianum. The characters given were 

 found in all cases, and still more strongly marked. These were the 

 smaller, lighter colored, apparently perfect, flowers — expanding in 

 the afternoon, gland bearing and nectariferous ; abundantly polli- 

 niferous, but vet infertile. And there were the larger, colored, 

 always-closed, and yet perfect flowers, resulting, without an apparent 

 exception, in perfect seeds. In many cases the styles are bent in the 

 bud, and the stigmas and anthers are brought together so as to 

 make self-fertilization absolutely certain. Many are in fact truly 

 cleistogamous. Occasionally with the growth of the fertilized 

 achenium, as noted in the case of P. Virginianum, the remains of 

 the pistils protrude through the floral envelopes, but this is not 

 always the case. 



In the light of so much that has been developed in connection 

 with the relations between insects and flowers, these studies of Poly- 

 goni present an intricate puzzle. Here are all the facts, positively 

 presented, required in the theory of cross-fertilization in this way. 

 There is nectar, perfect pollen in abundance, and insect visitors. 

 But there are no flowers to be fertilized. Those that are fertile — 

 the only fertile flowers are absolutely closed to the insects, — are in 

 fact cleistogamous. 



The following is the list of species on which these observations 

 are founded : — 



P. orientate L. P. Pennsylvanicum L., 



P. Persicaria L. P. Hydropiper L. 



P. acre, H. B K. P. Virginianum L. 



P. aviculare, L P. arifolium L. 



P. sagittatum L. 



