268 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In many Compositai the growth of the pistil coutiuues for a day 

 or two after the corolla has ceased to grow; in Zinnia the growth of 

 the floret is enormous on the last day, often doubling its length. 



Elasticity in the Filaments of Helianthus.* — T. Meehan points 

 out that in Uelianthus Icnticidaris Doulze, after the corolla tube has 

 reached its full length, the staminal tube commences to grow beyond 

 the mouth of the corolla and ultimately extends to about one-fourth 

 the whole length of the latter. The pollen, forced up by the growth 

 of the pistil within, then commences to emerge through the upper 

 portion of the staminal tube, which, the stamens narrowing, has the 

 apices free, till a large amount has accumulated at the apex of the 

 tube. The following day the arms of the pistil emerge and commence 

 to exjmnd, the staminal tube at once begins to descend, and by the 

 end of the third day has retired entirely within the tube of the corolla, 

 and with the pistil commences to wither. Throughout the whole 

 course the column of united anthers remains entirely of the same 

 length. It is the filaments only which are elastic. These stretch 

 fully one-half their leugth. The phenomenon is accompanied by a 

 change in the form of the floret. The extension of the staminal tube 

 is, the author considers, evidently mechanical, and is duo solely to 

 the upward growth of the stigma, which, partly it seems by the 

 incurved points of the stamens, and partly perhaps by the expansion 

 of the arms 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. The efiect of this 

 process is to render the plant strictly a self-fertilizer. Helianthus 

 hirsiitus exhibits similar features. 



Movements of Androecium in Sunflowers.f — Alluding to T. 

 Meehan's paper on the elasticity of the filaments of Helianthus,^ 

 Asa Gray says the retraction of the filaments is due to "automatic or 

 irritable shortening," as in the thistle tribe, and not to elasticity ; 

 nor is the anther-tube carried up to its full height by the elongation 

 of the style within, as may be readily tested by snipping off the 

 anther-tips wdth scissors when no retraction follows. Only after the 

 anther-tube has attained its full height is the tip of the style in contact 

 with the anther-tips. He also finds that (contrary to Mr. Meehan's 

 view) sunflowers are largely visited by bees, and by them cross-fertilized. 



Haustoria of Parasitic Phanerogams.§ — J. Schrenk describes the 

 mode of attachment of the root of several parasitic species oi Gerardia 

 to that of the foster-plant, Corylus rostrata. It is effected by means 

 of haustoria, which make their appearance as small tubercles on the 

 branches of the root, the cells of which are in oi)en communication 

 with those of the foster-root by the disappearance of the separating 

 walls. The merismatic active cells of the haustorium enter the 



* Proc. Acad. Nat. Sci. Philad., 1884, pp. 200-1 (2 figs.), 

 t Ibid., pp. 287-8. 

 j Supra, 



§ Bull. Torrey Bot. Club, xi. (1884) ] p. lOJ-H (1 pi.). 



