February 27, 1914] 



SCIENCE 



309 



ehromosomes have been counted in the 

 different developmental phases of nearly 

 all groups of plants. These counts have 

 shown that wherever there is sexual fusion 

 there is also, at some other point in the life 

 cycle, a reduction of the double number of 

 chromosomes so formed to the single num- 

 ber characteristic of the gametes. In all 

 cormophytes and many thallophytes this 

 reduction occurs at sporogenesis. 



The investigation of the complementary 

 phase of the chromosome behavior, the 

 doubling of the number at fertilization, has 

 during the past two decades also led to 

 extremely interesting results. 



The earlier workers on sexual nuclear 

 fusion apparently believed that the pater- 

 nal and maternal nuclear materials became 

 intimately mingled soon after contact of 

 the nuclear walls. Thus Klebahn (1892) 

 described the chromatin reticula of the two 

 nuclei as gradually merging into one, in 

 CEdogonium, and Shaw (1898) described 

 the same process in Onoclea. It is true 

 that Guignard (1891) had noted that, in 

 Lilium and Fritillaria, the male and female 

 reticula remain distinct until the prophase 

 of the first nuclear division of the embryo. 

 Later research, however, showed that the 

 paternal and maternal components remain 

 distinct till much later than this; in fact, 

 that the chromatin elements from the two 

 parents do not really fuse at all during the 

 process of fertilization. On the contrary, 

 it is pretty certain that all through the 

 development of the sporophyte the chromo- 

 somes from the two sources retain their 

 identity and individuality. 



Thus Blackman (1898) and Ferguson 

 (1901) say that in the fusing nuclei of 

 Pinus the two chromatin nets never lose 

 identity, and that at the first mitosis of the 

 embryo each constituent gives rise to its 

 own group of chromosomes. This inde- 

 pendence of the two chromatins at fertili- 



zation has since been seen in a number of 

 species, and it is now believed to persist 

 throughout the life of the sporophyte. The 

 double number of chromosomes is present 

 at each mitosis of this generation, and they 

 sometimes occur in pairs that are assumed 

 to consist of a paternal and a maternal 

 chromosome each. In certain plants also, 

 according to Overton (1909), Gregoire 

 (1910), Stout (1912) and others, the indi- 

 viduality of the chromosomes of the rest- 

 ing nucleus, postulated by Strasburger in 

 1894, is morphologically discernible. De 

 Vries (1903) emphasized this fact, that the 

 sporophyte, with its two complete sets of 

 chromosomes, is really two beings in one, 

 by designating it as the "2X generation." 

 This contrasts it at once, in this important 

 characteristic of chromosome number, with 

 the gametophyte or "X generation." 



Apparently then no actual fusion of the 

 chromosomes is included in the nuclear 

 union occurring at fertilization. The ques- 

 tion at once arising is: where in the life 

 cycle is there any fusion, or intimate union 

 of these inheritance-bearing units? The 

 answer to this question was for some time 

 generally believed to be offered by the phe- 

 nomena associated with the process of 

 "synapsis." Botanists had for some time 

 noticed and figured the peculiar contrac- 

 tion of the chromatin of the spore mother- 

 cell nucleus occurring just before the 

 chromosomes for the reduction division are 

 formed. Moore (1895) reaffirmed Stras- 

 burger 's view that, even with the best pres- 

 ervation, the chromatin regularly assumes 

 this condition at sporogenesis, and then 

 only. Moore, therefore, declared this eon- 

 dition to be, not an artifact, as many 

 workers had held, but a natural process, 

 which he named "synapsis." In spite of 

 the insistence by an occasional worker that 

 synapsis is an artifact, the impression of 

 its constancy and peculiarity grew more 



