LIFE HISTORY OF PINUS 33 



these chromosomes is correct, then both a quantitative and a 

 qualitative reduction of the chromosomes would occur in the 

 first or heterotypic division, and whole chromosomes, each 

 representing the half of a dual chromosome, would pass to 

 opposite poles. I am aware that such a phenomenon has been 

 described by Atkinson and a few others, but after long and care- 

 ful study there does not seem to me the least doubt, that, in the 

 case of the pines investigated, a longitudinal fission, and not a 

 transverse one, occurs in this first mitosis ; and X-, Y-, and 

 ring-shaped segments, as well as V's, pass to the poles, although, 

 as Belajeff has pointed out, they usually, because of their posi- 

 tion, have the form of V's in the anaphase of this divison. 



Most writers on sporogenesis, and especially those who are 

 advocates of the true reduction, have not found a resting nucleus 

 intervening between the heterotypic and the homotypic divisions. 

 As already stated a resting nucleus is clearly demonstrated at 

 this point in Pinus. The spireme formed from this nucleus 

 shows signs of longitudinal division before segmentation, and, 

 while lying at the equatorial plate, the two halves of each seg- 

 ment separate entirely, in most instances at least, before their 

 final orientation on the spindle. Now the question arises as to 

 whether or no this homotypic division effects a qualitative reduc- 

 tion. If the theory of the so-called " individuality of the chromo- 

 somes " is without foundation then it certainly does not ; but, if 

 the possibility of the complete rehabilitation of the chromosomes 

 be accepted, a qualitative reduction very probably does occur. 

 For under such conditions, the skein preceding the homotypic 

 division would consist of the daughter-chromosomes, formed as 

 a result of the heterotypic mitosis, fused end to end. These 

 daughter-chromosomes, it will be remembered, arose by the 

 longitudinal fission of a double chromosome and each, therefore, 

 consists of a pair of half chromosomes. Thus the second, 

 apparently longitudinal, splitting would effect the separation of 

 the half chromosomes of each pair, rather than the longitudinal 

 fission of a single chromosome. Reduction would thus take 

 place in the true or Weismann's sense. Because of certain 

 phenomena to be described in connection with the development 

 of the pro-embryo, I am inclined to believe that the chromo- 



