16 



The Journal of Heredity 



burj^cr also records numerous instances 

 in which he had Vjcen able to observe 

 the same mode of escape of the contents 

 of the pollen tube into the ripe embryo 

 sac in anj^iosperms. At last, as Stras- 

 burger puts it, in discussinj^^ fertilization 

 in the conifers: 



"The most important morphological 

 facts are clear. It is established that 

 the male nucleus that copulates with 

 the egj^ nucleus, ])asscs as such out of the 

 pollen tube into the ej^j^." 



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 jjrescnce of pollen on 

 the stigma is indispensable to seed- 

 formation. One chief reason why this 

 imjjortant jjroblem so long baffled all 

 investigators was the lack of pro])cr 

 methods of preparing material for study. 

 The older method of studying unfixed 

 and unstained sections had certain 

 advantages, it is true. The sequence of 

 developmental stages was often deter- 

 mined with certainty by actually follow- 

 ing their succession in living material 

 under the microscoijc, and there was 

 less cause also for dispute about arti- 

 facts. But structures of the same 

 refractive qualities were not readily 

 distinguished in such sections. As 

 Strasburger 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 i)ermittcd 

 the nuclei to be distinguished in the 

 strongh' refractive contents of the 

 pollen tube up to the moment of 

 fertilization." 



That these studies of 1884 were 

 successful was largely due to the use of 

 material fixed in .5% acetic acid, 1% 

 osmic acid or aljsolutc alcohol, and 

 stained in borax carmine, hematoxylin 

 or iodine green. 



The extreme significance of the fact 

 that those most highly organized por- 



tions of the cell substance — the nuclei — 

 were so ]jrominent in the ]jrocess of 

 fertilization was at once appreciated 

 by Strasburger, who in 1884 announced 

 the following general conclusions as the 

 outcome of his consideration 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 nucleus." 



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 observations of this nuclear 

 union at fertilization in each of the 

 great groups are the following, named 

 in the order of disco\-er\' : It was seen in 

 Pilularia (Campbell, 1888), in Riella 

 (Kruch, 1891), in GLdogonium (Klebahn, 

 1892), in the plant rusts (Dangeard and 

 Sapin-Trouffy, 1893), in the toad-stools 

 (Wager, 1893), in the red alga Nemalion 

 (Wille, 1894), in Sphcerotheca (Harper, 

 1895), in the rockwced, Fiicns (Farmer 

 and Williams, 1896). Finally Zeder- 

 bauer (1904) reported it for the Peri- 

 dinese, and Jahn (1907), Olive (1907) 

 and Kraenzlin (1907) made it out in the 

 myxomycctes. 



The observations just referred to, and 

 many others on plants in all groups, 

 warrant the general a]3ijlication of 

 Strasburgcr's conclusion that a nuclear 

 union is the characteristic feature of 

 every sexual ]3rocess. The few cases 

 where the male cyto])lasm seems more 

 prominent than usual, as in the three 

 conifers studied bv Coker (1903), Coulter 

 and Land (1905) and Nichols (1910), 

 can not yet be said to have rendered it 

 very i^robable that this cyto])lasm ])lays 

 a ])riniar\- ])art as an inlierilance carrier. 



