56 Colchicine 



A distribution study ior seven root tips showed that the regions away 

 from the tip contained hirgest number of polyploid cells. 



Reiteration of the c-mitosis in animals is limited by other factors, 

 such as toxicity to cells exposed over a long time. Also the balance 

 may be upset by increase in chromosomes per cell, so that only cells 

 with tetraploidy or octoploidy may survive. High numbers per cell 

 in animals have not been found as a consequence of c-mitosis. 



2.7-/; Recovery in plants. One remarkable feature about colchi- 

 cine is the ability of cells once stepped up to higher chromosome 

 numbers, to recover and thereafter produce new cells with the in- 

 creased niunber.'^*'' '^^^ ^0 In other words, tetrajjloid cells induced by 

 colchicine, if removed to water, will resimic nuclear mitosis with the 

 new increased numbers. 



A second notable point in the recovery process is the change tak- 

 ing place when cells with high chromosome numbers begin the re- 

 newal of the regular mitosis. If one hundred or more chromosomes 

 have aggregated in one cell and colchicine is removed, soon the 

 chromosomes gather into small groujjs giving the effect of many star 

 metaphases. Each of these groups may be the focal point around 

 which a new cell is formed (Fig. 2.6) . By a process of multipolar 

 divisions the large numbers in a cell become reduced to smaller num- 

 bers. '^'^ 



The length of treatment at a given concentration determines the 

 speed of recovery based upon the types of metaphase chromosome 

 formations observed. A one-hour treatment of Spinacia in 0.25 per 

 cent shows complete recovery in 48 hours. A five-hour treatment at 

 0.25 per cent requires 63 hours for recovery.''' 



2.7-2.- Recovery in animals. Interphase from star metaphase with- 

 out an anaphasic movement took place in corneal epithelial cells as 

 these tissues recovered from a strong dosage under a short exposure 

 period. ^^9 Multiple stars appeared after five and six days from the 

 time of the last application of colchicine. 



Siredon cells show another phenomenon reported many times in 

 other material, the swelling of chromosomes and cytoplasm. The 

 immobile chromosomes seem to swell while in a scattered arrange- 

 ment. "^^ This is similar to reversal of prophase; later the chromosomes 

 fuse into an interphasic nucleus (Fig. 2.9) . Similar reconstructions 

 during recovery are to be found in regenerating liver cells of the rat 

 (Fig. 2.12) .'-^ A progressive fusion of micronuclei reduces the num- 

 ber until trinucleate and binucleate cells develop. Tissue cultures 

 show comparatively the same micronuclear development.^^- ^^ 



Partial c-mitoses and multiple stars are common during recovery 

 as observed in neuroblasts.'^" The multiple stars are evidence that 

 recovery processes are imder^vay. 



