494 BULLETIN OF THE 



Hertwig, place much confidence in this observation of normal develop- 

 ment after such fecundation. A fusion of sperm nuclei is not to be 

 seen ; on the contrary they are mutually repelled by their astral rays. 



Extensive studies on the nature of fecundation among plants lead 

 Strasburger ('77) to a modification (p. 483) of his previously expressed 

 views,"* for he now holds that not all of the contents of the pollen tube 

 are taken up by the egg nucleus, but that a part of it becomes directly 

 mingled with the protoplasm of the egg. It now appears improbable 

 to him that the portion of the fecundating substance which is destined 

 for the egg nucleus can be appropriated by the latter in the amorphous 

 condition in which it enters the egg, without having first assumed the 

 form of a nucleus. This view is then generalized and sharply formulated 

 (p. 508) as follows : '' It is the equivalent parts of both cells which are 

 united in fecundation." Support is afforded this view by the process of 

 copulation in the " Gameten " of Acetabularia and Spirogyra, in the 

 conifers, and especially in the case of those metasperms whose egg 

 nucleus contains only a single nucleolus, and where the sperm nucleus 

 in like manner embraces only a single nucleolus. For he finds that in 

 such cases (e. g. Monotropa, pp. 488, 489, Taf. XXX. Figs. 127-129, 131- 

 133, 135, 138) the new cell nucleus (male pronucleus) and the egg nucleus 

 unite without the disappearance of their nucleoli, so that two nucleoli, 

 which ultimately unite, are distinguishable for a considerable time within 

 the conjugated nuclei. This is the more noticeable in the case of Mono- 

 tropa from the fact that the male pronucleus and its nucleolus are 

 constantly somewhat smaller than the corresponding egg nucleus and 

 nucleolus. The division of the pollen cell shortly before fertilization, 

 from which result a greater and a smaller ("vegetative") cell, is found 

 by Strasburger to hold true with metasperms (p. 450) as well as with 

 archisperms. With the formation of the pollen tube the nuclei of both 

 migrate — the nucleus of the large cell foremost — usually into its tip 

 (p. 456), where they take part in fecundation. But in the archisperms 

 the " vegetative " cell is resorbed while the nucleus of the larger cell 

 migrates to the tip of the pollen tube and there undergoes successive 

 divisions, — two or more. The tip of the pollen tube is never broken 

 through. Its protoplasmic contents are thought (pp. 483, 490) to pass 

 both the membrane of the pollen tube and that of the embryo-sac, 

 not in a diosmotic way, but directly, as a homogeneous viscid mass. 

 The same force which has impelled the protoplasm during the growth of 

 the tube toward its tip now causes it to advance in the direction of (i. e. 



* See Strasburger '76, pp. 308, 309, and '76", p. 402. 



