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INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



the 2ft X 4ft cross from an incompatible to a compatible one in an 

 ingenious way. Treatment with colchicine usually results in peri- 

 clinical chimeras in Datura. Some of these have the doubled chro- 

 mosome number in the epidermal layer but not in the underlying 

 tissues. Since it is the epidermal layer which forms the trans- 

 mitting tissue in the style in Datura, a periclinal chimera with a 

 4n epidermis should react exactly like a pure 4n parent so far as its 

 relation to pollen tubes from a 4ft male parent is concerned. This 



Fig. 204. Method of removing embryo from seed of 7ns with help of sterile needle. 

 (After Randolph, 1945.) 



was actually found to be the case, and diploid pollen tubes from 

 4ft males grew readily without bursting in styles of a periclinal 

 chimera with a 4n epidermis. 



Finally, there remains the difficulty that even after the pollen 

 tubes have reached the ovary and ovules, fertilization may fail to 

 occur for some obscure reason. To mention one example, when 

 the flowers of Ribes nigrum are self -pollinated, the pollen tubes 

 enter the ovules and "even lay themselves against the embryo-sac 

 nucleus" but the male and female nuclei do not fuse and hence no 

 seeds are formed (Ledeboer and Rietsema, 1940). Since there is 



