Nucleus and Chromosomes 39 



limited. In light of the complex interaction, it would seem that the 

 kinds of metaphase that could develop would be more extensive. 



2.7-2; The oriented arn'sted metaphase. In 1889, Pernice^^ 

 sketched the first star metaphase, a distinctive oriented type induced 

 by colchicine.'"' Next, these were reported in 1936*'i among tissues of 

 mice and carcinomatous tissue cultures,*"'- and since then the oriented 

 star metaphase has been published many times, from a great variety 

 of biological specimens. 



The frequency of star metaphases is far too regular to be ascribed 

 to a random occmrence.i- "-' The chromosomes are all drawn to one 

 focal point with the proximal jjortions extended outward resembling 

 a star, and the type was named accordingly. The centromeric por- 

 tions of the chromosomes are congregated at this one focal point^ 

 (Figs. 2.5, upper left, and 2.1B-F) . 



Two sets of data from similar materials, Triton vulgaris'^ and 

 Triturus viridescens,'^ respectively, are pertinent to the matter of 

 origin of the star. Larval cells of Triton were kept in solutions and 

 were then removed from time to time, fixed, and stained for chromo- 

 somal pictures. The star, or oriented, metaphases, exceeded the un- 

 oriented types in the first fixations, at three hours (Table 2.2) . The 

 Triturus corneal cells, fixed and stained at intervals during recovery 

 from the effects of drug, do not show the star metaphases at their 

 peak initil twenty-four hours have elapsed (Table 2.2) . 



Two critical experiments performed with neuroblastic cells in the 

 grasshopper explain some of these differences.-^'* Strong concentrations 

 applied when the cell w^as at metaphase led to a star metaphase (cf. 

 Chapter 3; Fig. 3.20) . This action occurred after a particular mitotic 

 stage had been reached. Another route was used to produce the star 

 in neuroblastic cells, viz., application of lower dosage (1.9 X ^^~^' ^^^) 

 at late prophase. Two sets of factors were operating: the concentra- 

 tion and the mitotic stage. In one instance a metaphasic stage was 

 used, and in the other, prophase. Each required a different concen- 

 tration. In the Triton materials, strong concentrations acted early, 

 yet in Triturus, the stars accunudated later as cells were recovering 

 from a previous strong dose. We shall return to this problem again 

 inider the subject of spindle mechanisms. 



Multiple stars in single cells are commonly found in AlJiu7n root 

 tips when cells recover.'-''- *'■' In similar instances, the "multiple" stars 

 (Fig. 2.6) are to be seen in the Tubifex eggs."'' Among the Triturus, 

 recovery stages at six days show multiple stars (Fig. 2.7) . Multiple 

 stars are formed in connection with transition stages from the full 

 c-mitosis to the complete recovery of the bipolar mitosis.^*' 



Distorted star metaphases'^ are asymmetrical figures (Fig. 2.5) . The 

 origin of distorted star metai)hase is controversial, and although they 



