K. — BOTANY. 187 



recently emphasised by Gates,-'' who attributes the peculiarity of the 

 lata mutation in CEnothera (which has arisen as a modification at 

 different times from each of three distinct species) to an irregularity 

 in meiosis in the germ mother cells whereby one daughter cell receives 

 an extra duplicate chromosome while the sister cell lacks this chromo- 

 some. The cell with the extra chromosome fertilised by a normal germ 

 produces a lata individual. On the chromosome view every normal 

 fertilised egg contains a double set of chromosomes, each carrying a 

 complete set of the factor elements. Hence, if some of the one set 

 become eliminated we can still imagine that a noraial though under- 

 sized individual might develop. The converse relation where increased 

 size goes with multiplication of chromosomes was discovered by 

 Gregory,"^ in a Primula, and occurs also in CEnothera gigas, a mutant 

 derived from CE. Lamarckiana. Gregory found in his cultures giant 

 individuals which behaved as though four instead of two sets of factors 

 were present, and upon examination these individuals were found to 

 contain twice the normal number of chromosomes. It is interesting 

 in this connection to recall the results obtained by Nemec^* as the 

 result of subjecting the root tips of various plants to the narcotising 

 action of chloral hydrate. Under this treatment cells undergoing 

 division at the time were able to form the daughter nuclei, but the 

 production of a new cell wall was inhibited. The cells thus became 

 binucleate. If on recovery these cells were to fuse before proceeding 

 to divide afresh a genuine tetraploid condition would result. So few 

 cases of natural tetraploidy have so far been observed that we have as 

 yet no clue to the cause which leads to this condition. 



The conclusions to which we are led by the considerations which 

 have here been put forwaid are, in the main, that we have no warrant 

 in the evidence so far available for attributing special hereditary pro- 

 cesses to the cytoplasm as distinct from the nucleus. On the other 

 hand, there is a very large body of facts pointing to a direct connection 

 between phenotypic appearance and chromosomal behaviour. In 

 animals the evidence that the chromosomes constitute the distributional 

 mechanism may be looked upon as almost tantamount to proof; in 

 plants the observations on Drosera, Primula, CEnothera, Sphcerocarpus 

 are in harmony with this view. "When we come, however, to the 

 question of linkage and general applicability of the conception of 

 ' crossing over ' as adopted by Morgan and his school we are on less 

 ^ certain ground. In Drosophila itself, the case which the scheme was 

 framed to fit, the entire absence of ' crossing over ' in the male remains 

 unaccounted for, while the evidence from certain plant types appears 

 to be definitely at variance with one of its fundamental premises. If 

 segregation at the recognised reduction division is definitely established 

 for animal types, then we must conclude that the sorting-out process 

 may follow a different course in the plant. 



The question as to what is the precise nature of the differences for 



-^ NoAv Phytologist, vol. xix., 1920. 

 '* Proc. Boy. Soc. vol. Ix.xxvii. b, 1914. 



-5 Jahrb. f. iriss. Bot.. xxxix., 1904, 'Das Problem der Begruchtungsvor- 

 gange,' 1910. 



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