14 JOURNAL op- THE [January, 



ovule and eventually reach the corpuscula. * * * * 

 The union of the protoplasm of the pollen-tube with that of the 

 germ-cell appears to take place by diffusion through the wall of 

 the former, as no openings in it have been discovered." He 

 refers to the fecundation of Angiospermai in the following lan- 

 guage,'^* illustrating the process by a figure of the fertilized ovule 

 of Viola tricolor taken from Sachs : — 



" Fertilization takes place as follows : The pollen grain, resting 

 upon the moist surface of the stigma, absorbs moisture and ger- 

 minates, sending out a tube which penetrates the soft tissues of 

 the stigma and style, finally reaching the cavity of the ovary, 

 where it enters the micropyle of an ovule." 



Dr. William B. Carpenter's treatment of this subject is clear 

 and concise. " The tracing downwards of the pollen-tubes 

 through the tissue of the style may be accomplished by sections 

 (which, however, will seldom follow one tube continuously for 

 any great part of its length), or, in some instances, by careful 

 dissection with needles. Plants of the Orchis tribe are the most 

 favorable subjects for this kind of investigation ; which is best 

 carried on by artificially applying the pollen to the stigma of 

 several flowers, and then examining one or more of the styles 

 daily. ' If the style of the flower of an Epipactis (says Schacht), to 

 which the pollen has been applied about eight days previously, 

 be examined in the manner above mentioned, the observer will 

 be surprised at the extraordinary number of pollen-tubes, and he 

 will easily be able to trace them in large strings, even as far as 

 the ovules. Viola tricolor and Ribes nigrum and rubru?n are 

 also good plants for the purpose ; in the case of the former plant, 

 withered flowers may be taken, and branched pollen-tubes will 

 not unfrequently be met with.' The entrance of the pollen-tube 

 into the micropyle may be most easily observed in Orchideous 

 plants, and in Euphrasia ; it being only necessary to tear open 

 with a needle the ovary of a flower which is just withering, and 

 to detach from the placenta the ovules, almost every one of 

 which will be found to have a pollen-tube sticking in its micro- 

 pyle."^* 



The artificial branching of pollen-tubes has been well illustra- 

 ted and described by S. Reisseck.*^ 



"Loc. cit.,p. 423. 



«*"The Microscope and its Revelations," 6th Edition, 1881, pp. 464, 465. 



"Acta Acad. Leopold Carol. Nat. Cur., XXI., Pt. 2, pis. XXXIV., XXXV. 



