526 SIGNIFICANCE OF CAMBIUM 



cells during different stages in ontogeny and under different environ- 

 mental conditions. Conklin has emphasized the fact that in many- 

 cases the size of the nucleus is determined by the volume of proto- 

 plasm in which it lies, rather than by the number of chromosomes. 



On the botanical side, Gates, Gregory, Winkler, and Tupper and 

 Bartlett have shown that a number of races of plants, which 

 have the tetraploid, instead of the diploid, number of chromo- 

 somes, are composed of cells larger than those of normal varieties. 

 Winkler's paper is a particularly suggestive one, not only owing to 

 the interesting experimental methods used in his work, but to his 

 general discussion of the relation between cell size and chromosomal 

 number in plants. He reaches the following conclusions, as a result 

 of his own observations and those of a number of other investiga- 

 tors. In embryonic somatic tissue, terminal and lateral meristems, 

 the cells are of nearly uniform size, are roughly isodiametric, and 

 under normal conditions contain the diploid mmiber of chromo- 

 somes. Multinucleate protoplasts, nuclear fusions, and changes 

 from the diploid to the tetraploid and polyploid condition are of 

 common occurrence in non-meristematic somatic tissue. In the 

 latter tissue many cells depart widely from the inherited specific cell 

 size of the plant. Such cells tend to be hyperchromatic ; much elon- 

 gated elements containing more than one nucleus each, and other 

 types of large cells an abnormal number (tetraploid or polyploid) of 

 chromosomes. In other words, Winkler considers that there is a 

 very significant correlation between cell size and chromosomal mass, 

 both in the embryonic and non-meristematic somatic tissues of 

 plants. 



As I have suggested at the beginning of this paper, the cambium 

 appears to possess certain distinct advantages as a medium for study- 

 ing various phases of the nucleocytoplasmic-relation. In this tissue ad- 

 jacent cells vary greatly in shape and size and it is possible not only to 

 compare elongated initials of very different lengths and volumes, but 

 also to contrast them with adjoining ray initials which are of the same 

 general order of magnitude as the cells of the embryo and terminal 

 meristems. By proper experimental methods the long initials may be 

 induced to divide into smaller and smaller units, until more or less 

 isodiametric cells, which resemble the ray initials, are formed. These 



