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1920] BRIEFER ARTICLES 349 



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non, and in any two consecutive seasons an individual tree may shed 

 pollen on dates separated by a corresponding interval of time. In the 

 same way it has been found impossible to predict with any degree of 

 accuracy the time of occurrence of any of the significant stages in matura- 

 tion, and this fact has rendered more difficult the determination of 

 chromosome number in S. sempervirens. Numerous efforts so far 



have failed to discover the reduction divisions in the microspore mother 

 cells. 



As to chromosome number in S. sempervirens, Lawson remarks 

 that "as near as could be estimated, there are 16 chromosomes in the 

 gametophyte and 32 in the sporophyte." In recent tabulations of 

 chromosome numbers in plant species, 45 gymnosperms are listed. 

 All but 12 of these have x 12, and 2X 24, and of these 12 (x 16 and 2X 32) 

 a number are listed as doubtful. On this basis perhaps there might 

 be legitimate ground to question Lawson's count. In sections of 

 root tips of S. sempervirens we have made counts which only in rare 

 instances confirm Lawson's report. The difficulties are great in such 

 material, however. In corresponding and more favorable material of 

 S. gigantea, we have uniformly counted from 21 to 24 chromosomes, 

 but never a greater number. 



With these facts in mind, the following possibilities present them- 

 selves. First, if Lawson's count is correct for S. sempervirens and if 

 our count is correct for S. gigantea, the two species have different chromo- 

 some numbers. Second, if our suspicion of Lawson's count in 5. semper- 

 virens is valid and if our count in 5. gigantea is correct, both species 

 have #12 and 2X 24. The third possibility involves an inaccuracy in 

 our count of S. gigantea and chromosome numbers 16 and ^2 for both 

 species. In our opinion the second possibility is the only one which 

 merits serious consideration. It seems worth while, however, to present 

 the whole situation, since the other possibilities cannot wholly be left 

 out of account with the data at hand. Further studies will involve 

 an investigation of the life history of S. gigantea and the obtaining of 

 a final conclusion as to chromosome number in 5. sempervirens. — T. H. 

 Goodspeed and M. P. Crane, University of California. 



