1884.] NATURAL SCIENCES OP PHILADELPHIA. 201 



whole of this space. This pollen could fall onthestigmaof theflower 

 of the previous day, but as the stigma is already covered by pollen 

 of its own, other pollen is hardly likely to be of much service ; and 

 even if this outer circle did profit by the pollen of the inner, it would 

 not be cross-fertilization in an}^ legitimate sense of the word. We 

 may say emphatically that the arrangements favor self-fertilization. 



An interesting feature is the change in the form of the floret 

 on the second day of expansion. At the point where the stamens 

 are inserted on the corolla, the tube is somewhat inflated and 

 covered by short hair. On the first day this inflated portion is 

 elongated, and the whole tube luiiformly cylindrical, as in fig. 1. 

 On the second day the inflation is depressed, and the corolla 

 hypocrateriform as in fig. 2, This is probably owing to the 

 partial withering of the corolla, but it is worth noting as a guide 

 in the study of the florets of compositte — the normal form is that 

 exhibited before the anthers mature. 



The extension of the staminal tube is evidently mechanical, 

 and is due solely to the upward growth of the stigma, which, 

 partlj' it seems by the incurved points of the stameus, and 

 partl}^ perhaps b^'^ the expansion of the arras of the pistil, is able 

 to carry the tube up with it. This force being removed as soon 

 as the arms emerge, the elastic stamens draw the tube down 

 again to its normal location. This portion of the observation 

 was made by Mr. Alois Lunzer, the artist of the Flowers and 

 Ferns of the United States, then engaged in making a painting of 

 the flower for that work. 



The eflect of this process is to render the plant strictly a self- 

 fertilizer. The arms of the pistil are covered with rigid hair 

 having an upward direction. By the pushing upwards of the 

 pistil in its endeavor to escape from the embrace of the stamens, 

 these hairs brush the pollen upwards, and it is in this way that 

 the pollen is forced through the fissures at the apex as already 

 described. When the arms emerge, they are completely covered 

 with own-pollen, which remains till the stigmas mature. 



Helianthus lenticularis is the common annual sunflower of the 

 Western plains, and believed by Professor Asa Gray to be the 

 parent of the garden sunflower. This is not in bloom at the 

 present date. One species, Helianthus hirsutus, is in bloom, and 

 exhibits similar features, and the}^ are probably characteristic of 

 the whole genus, and perhaps of other composite plants. In 

 Centaurea the apex of the anther tube is closely united, and is 

 taken up with the development of the pistil, which finally escapes 

 through a rupture at the side. But in this case there seems to be 

 a cotemporaneous growth of the filaments. At any rate there is 

 no elasticity, and the staminal tube is not drawn back to the tube 

 of the corolla. Pollen is, however, brushed out b}^ the stigmatie 

 hair, and each floret receives own-pollen as in Helianthus. 



The following was ordered to be printed : — 

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