Darling; Sex in dioecious plants ^ 191 



some species the chromatin is contained in the nucleolus and in 

 some apparently not ; where it is thus contained the chromatin 

 seems to be transferred by the thread becoming attached to the 

 nucleolus. Cardiff ('06) figures a bud-hke process attached to the 

 nucleolus of Acer platanoides and thinks that it illustrates the 

 manner of transfer of the chromatin from the nucleolus to the 

 spireme thread. I have observed in the pollen mother cells of 

 Zea Mays these bud-like processes which I believe to function in 

 the same way. As to the manner in which the chromatin is trans- 

 ferred to the thread, I find, however, no case in plants, which has 

 been thoroughly investigated, that corresponds to the condition 

 reported in this paper, although this method of transference may 

 not be uncommon. 



Cytologists are practically unanimous in the belief that the 

 chromosomes in plants are formed by the segmentation of the 

 spireme thread. The only process analogous to the formation 

 of the five chromosomes which come out of the nucleolus in Acer 

 Negundo is that found In the formation of the Idlochromosomes 

 in insects. It might be urged that the case is not analogous, be- 

 cause In Acer Negitndo all of the chromatin is contained in the 

 nucleolus and that these five chromosomes are merely delayed In 

 their formation ; nevertheless the significant fact remains that the 

 formation of these five is different from that of the other eight In 

 that they come from the nucleolus already formed. It Is to be 

 noted, moreover, in insects that sometime during the life history 

 of these idlochromosomes they are contained In a chromatin 

 nucleolus, and in many cases they are at some period associated 

 with the true nucleolus or plasmosome. So far as the observa- 

 tions go, this case oi Acer Negimdo seems to correspond In a gen- 

 eral way to those insects which Wilson Includes In Class I, where 

 the two kinds of spermatozoa contain idiochromosomes of the same 

 number and of the same size. The evidence at present is far too 

 meager to warrant any definite conclusion as to the nature of the 

 five chromosomes, which are somewhat suggestive of Idlochromo- 

 somes in the manner of their formation. 



The common occurrence of the difference In behavior of the 

 chromatin in the two nuclei attracted my attention from the first 

 and led me to examine the phenomenon with a view to determine 



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