310 



SCIENCE 



[N. S. Vol. XXXIX. No. 1000 



general at the end of the last century. Then 

 in 1901 Montgomery suggested that it is in 

 this process that the long-delayed union of 

 the paternal and maternal chromatin 

 occurs. Montgomery's conception, that 

 each of the double or bivalent chromo- 

 somes, formed on emergence from synapsis, 

 is made up of a paternal and a maternal 

 chromosome, which have in some way been 

 paired up during the synaptic process, 

 came to be rather generally accepted. 



Recently, however, a number of workers 

 have dissented vigorously from the view 

 that synapsis is a constant, or a highly 

 significant process. Thus Gregoire (1910), 

 Gates (1911) and Lawson (1912) hold that 

 it does not occur unfailingly at sporo- 

 genesis. Lawson says that so much of the 

 separation of the chromatin from the nu- 

 clear waU as is not due to artifact is attrib- 

 utable to the more rapid growth of the 

 nuclear wall than of the chromatin. 

 Finally all three agree that such a process 

 is not needed for the pairing of the chromo- 

 somes, since, as was observed by Stras- 

 burger (1905) and others, the chromo- 

 somes may regularly appear in pairs in the 

 vegetative mitoses of the sporophyte. 

 Moreover studies of the vegetative nuclei 

 of the sporophyte, especially by Gregoire 

 and his students, show that their chromo- 

 somes are closely connected by adhesions, 

 and by pseudopodium-like strands developed 

 between the viscid chromosomes when the 

 new reticulum is formed after each mitosis. 

 Gates (1911) after reviewing recent work 

 on this point holds that the pairs seen in 

 vegetative mitoses are of a paternal and a 

 maternal chromosome each. He sees no 

 adequate reason for thinking that the asso- 

 ciation of parental chromosomes at synap- 

 sis is any more intimate than that which 

 occurs, as he says, " at or soon after fertili- 

 zation." He evidently regards the con- 

 nections between sporophytie chromosomes 



referred to above as affording ample oppor- 

 tunity for any interchange of material or 

 "influences" between the chromosomes. 

 Gates does not say just when the parental 

 chromosomes are first paired up after fer- 

 tilization nor give the evidence for this. 

 He fails, also, to explain the fact, upon 

 which practically all workers seem agreed, 

 that the halves of the diploid chromosomes 

 are associated with each other in a more 

 intimate way than the chromosomes of any 

 other mitosis in the life cycle. 



VI. ALTERNATION AND CHROMOSOME NUM- 

 BERS IN THE AIjGJE, 1896- 



We have already seen that an attempt 

 was made in the third quarter of last cen- 

 tury to interpret the life histories of cer- 

 tain thallophytes, especially among the 

 algae, in terms of the alternating genera- 

 tions discovered by Hofmeister among the 

 arehegoniates. The basis of comparison 

 was the occurrence of a sort of polyembry- 

 ony at the germination of the sexually pro- 

 duced oospore of these algee. There was 

 much uncertainty, however, concerning the 

 real correspondence of phases in the two 

 groups, and even as to whether the alterna- 

 tion was of the same sort in the two groups. 



With the promulgation of Strasburger's 

 view (1894) regarding the significance of 

 the reduction of the chromosome number 

 in the life cycle, botanists felt that they 

 would now be able to distinguish the phases 

 of a real alternation of generations wher- 

 ever chromosomes could be counted. A 

 number of workers therefore followed out 

 cytologically the details of development 

 and conjugation of the sexual cells, and 

 the germination of the zygote in various 

 algse. 



The work of Chmielewski (1890), on 

 Spirogyra, and of Klebahn (1891) on des- 

 mids showed some indications of a reduc- 

 tion process at the germination of the 



