350 



METHODS IN PLANT HISTOLOGY 



1915, Karsten made a comparatively extended study of periodicity in 

 various stems and roots, together with notes on algae. 



It is safe to say that the maximum number of mitoses in root-tips 

 will be found shortly after noon (1 :00 p.m.) and shortly before mid- 

 night (11 :00 P.M.). It is certain, however, that abundant mitoses may 

 be found at other times — even at 3:00 p.m. — in sporangia of ferns, in 



B 



D 



Fig. 122. — Nuclear and cell division in root-tip of onion. .4, resting nucleus; B, spirem stage; 

 C, spirem divided into chromosomes; D, metaphase, with chromosomes split; E, late anaphase; F, 

 early telopha.se; G, late telophase; H, resting nucleus. X 1,200. From Chamberlain's Elements of 

 Plant Science (McGraw-Hill Book Co., New York). 



anthers of angiosperms, in endosperm, and in free nuclear stages of the 

 embryo of gymnosperms. 



Mitotic figures play such an important part in the development of 

 the plant and in modern theories of heredity that it is worth while to 

 acquire a critical technique in fixing and staining these structures (Fig. 



122). 



During the past two years we have made an extensive series of 



