FEBR0ABT 27, 1914] 



SCIENCE 



305 



one male nucleus fusing with that of the 

 egg. In the same publication Strasburger 

 also records numerous instances in which 

 he had been able to observe the same mode 

 of escape of the contents of the pollen tube 

 into the ripe embryo sac in angiosperms. 

 At last, as Strasburger puts it, in discuss- 

 ing fertilization in the conifers: 



The most important morphological facts are 

 clear. It is established that the male nucleus 

 that copulates with the egg nucleus, passes as 

 such out of the pollen tube into the egg. 



Thus, finally, was the actual material 

 contribution of both parents to the embryo 

 of the seed plants first seen. This was just 

 two centuries, lacking a decade, after 

 Camerarius (1694) had proven that the 

 presence of pollen on the stigma is indis- 

 pensable to seed formation. One chief rea- 

 son why this important problem so long 

 baffled all investigators was the lack of 

 proper methods of preparing material for 

 study. The older method of studying un- 

 fixed and unstained sections had certain ad- 

 vantages, it is true. The sequence of devel- 

 opmental stages was often determined with 

 certainty by actually following their suc- 

 cession in living material under the micro- 

 scope, and there was less cause also for dis- 

 pute about artifacts. But structures of the 

 same refractive qualities were not readily 

 distinguished in such sections. As Stras- 

 burger himself says (1884, p. 18) : 



The negative results of my earlier studies and 

 of those of Elfving were due to the lack of a 

 method which permitted the nuclei to be distin- 

 guished in the strongly refractive contents of the 

 pollen tube up to the moment of fertilization. 



That these studies of 1884 were success- 

 ful was largely due to the use of material 

 fixed in five-ten ths-per-cent. acetic acid, 

 one-per-cent. osmic acid or absolute alcohol, 

 and stained in borax carmine, hematoxylin 

 or iodine green. 



The extreme significance of the fact that 

 those mast highly organized portions of the 



cell substance — the nuclei — were so promi- 

 nent in the process of fertilization was at 

 once appreciated by Strasburger, who in 

 1884 (p. 77) announced the following gen- 

 eral conclusions as the outcome of his con- 

 sideration of the phenomena observed : 



(1) The fertilization process depends upon the 

 copulation with the egg nucleus of the male 

 nucleus that is brought into the egg, which is in 

 accord with the view clearly expressed by O. 

 Hertwig. (2) The cytoplasm is not concerned in 

 the process of fertilization. (3) The sperm 

 nucleus like the egg nucleus is a true cell nu- 

 cleus. 



In the years since 1884 the nuclei have 

 been found to be the structures chiefly 

 concerned in fertilization whenever such a 

 process occurs. Among the earlier obser- 

 vations of this nuclear union at fertiliza- 

 tion in each of the great groups are the 

 following, named in the order of discovery : 

 It was seen in Pilularia (Campbell, 1888), 

 in Riella (Kruch, 1891), in CEdogonium 

 (Klebahn, 1892), in the plant rusts (Dan- 

 geard and Spain-Trouffy, 1893), in the 

 toad-stools ("Wager, 1893), in the red alga 

 Nemalion (Wille, 1894), in Spharotheca 

 (Harper, 1895), in the roekweed, Fucus 

 (Parmer and Williams, 1896). Finally 

 Zederbauer (1904) reported it for the Peri- 

 dineaj and Olive (1907) and Kraenzlin 

 (1907) made it out in the myxomycetes. 



The observations just referred to, and 

 many othei's on plants in all groups, war- 

 rant the general application of Stras- 

 burger 's conclusion that a nuclear union 

 is the characteristic feature of every sexual 

 process. The few cases where the male 

 cytoplasm seems more prominent than 

 u.sual, as in the three conifers studied by 

 Coker (1903), Coulter and Land (1905) 

 and Nichols (1910), can not yet be said 

 to have rendered it very probable that this 

 cytoplasm plays a primary part as an in- 

 heritance carrier. 



