Cellular Growth 117 



II the microspore nucleus is treated with colchicine, h typical c- 

 mitosis appears. Since the haploid numbers prevail, an otherwise 

 precise picture of the c-mitosis can be obtained. A diploid uninucleate 

 pollen grain is formed after the c-mitosis (Fig. 4..S) . 



When monad microspores with numbeis higher than haploid 

 divide without colchicine, some interesting cells are formed. 1 hese 

 may be regarded as an aftereffect of colchicine. Multipolar divisions 

 are common, and in jxirticular, a tripolar division gives rise to a huge 

 grain, with two vegetative cells apj)resscd close to the wall, and one 

 generative cell. On occasion, two generati\e cells are formed."*' These 

 conditions are similar to the recovery phases described in earlier 

 chapters. 



Pollen grains of Polygonatum with one generative cell, a haploid, 

 and a tube cell were tested for c-mitotic characteristics (Fig. 4.2) F' 

 The method of testing is described in detail in Chapter l(i. In Chap- 

 ters 2 and 3. illustrative material was drawn from pollen tube c- 

 mitosis, but here it is pertinent to point out that the c-mitosis in this 

 structure never exceeds the diploid number. Very rarely do the c- 

 pairs become completely separated, so reversion to the interphase goes 

 from an arrested metaphase rather than through c-anaphase. Enough 

 tests have been run to rcj^ort conclusively that there is a termination 

 to c-mitosis and. unlike the divisions in root tips that continue to 

 build high numbers, multiple-ploidy has never been found in pollen 

 tubes with Polygonal inn or reported from other sources. Then the 

 microgamctophyte never exceeds dijjloidy. 



In the case of embryo sac development in Tradescautia, the nuclei 

 that icgularly divide during the process of gametojihyte formation 

 seem to build up the amount of chromatin, although as is expected, 

 no spindle forms with colchicine. Therefore, the chromosomes re- 

 main together. The si/e of the large nucleus, the size of the embryo 

 sac, and a tendency toward cell formation lead one to infer that c- 

 mitoses proceed to but do not go beyond the eight-cell condition, nor- 

 mal for an embryo sac in Tradescantia (Fig. 4.6) . Aside trom the c- 

 mitotic aspect, the unusual increase in the embryo sac beyond that 

 for the control is of interest in light of our discussion about the action 

 of colchicine on growth ])rocesses involving increase in volume. ^^"^ 



71ie ovules of Cart ham us tinctorius did not develop into seeds, 

 and no descriptive cytology accompanied the successive stages that 

 must have taken place when colchicine acted while the embryo sac 

 stages were in foiniation. This would be of interest for a comparison 

 with Tradescantia.'-''- "•* 



^.3-1: (Uunetophytcs of mosses, liiu-rn'oyts, and ferns. In n)()8, a 

 series of experiments with mosses demonstrated that polyploidy could 

 be induced artificially. Fhe Marchals used regenerative tissues to iso- 

 late polvj)loid races. Three decades elapsed between the fust work 



