I. W. BAILEY 



527 



may subsequently elongate and regenerate elements of normal size. 

 In regions having cold winters, there is a more or less prolonged rest- 

 ing period, during which the cambial cells are inactive (not under- 

 going division). This period offers a favorable opportunity for 

 measuring and computing the relative sizes of the initials and their 

 nuclei. Furthermore, during the active growing season, adjacent 

 cells (ray initials and elongated initials of varying sizes) may be 

 found in equivalent stages of karyokinesis and cytokinesis, which 

 facihtates comparisons within the limits of a single section. 



TABLE I. 



Pinus strohus L. 



Type. 



Ray initials. 

 Large 



Ray initials. 

 Large 



Nucleus. 



Dimensions. 



<! > 



Cell. 



Dimensions. 



Approximate 

 volume. 



■330 



^ s 



) o > 

 1 



' S QT3 

 J 3 cd o 



Cambium from 1 yr. old stem. 



cu. mtcra 



5,000 

 60,000 



Cambium from 60 yr. old stem. 



12.4 

 82 



12.5 

 5.9 



9.9 

 8.9 



850 

 3,500 



24. 

 4,000 



26.6 

 6.2 



17.0 



42.4 



10,000 

 1,000,000 



1:14 

 1:60 



1:12 

 1:286 



Basis: dimensions of cells and nuclei are averages of 50 measurements. 



In 1917, 1918, and 1919, the writer collected numerous specimens 

 of the cambium of Pinus strohus L. — from different parts of the stem 

 and root, from trees of different ages and sizes, and from varying 

 environments— at frequent intervals during the resting and growing 

 seasons. As shown in Table I and in Figs. 1 to 6, the larger initials of 

 the common white pine tend to have larger nuclei, but the ratio between 

 cell size and nuclear size fluctuates greatly in the case of the elongated 

 initials. So far as I have been able to determine, however, all the nu- 

 clei, regardless of their size, contain approximately the diploid number 

 (twenty-four) of chromosomes. The larger size of the elongated 



