32 Genetic Studies in Potatoes: Sterilitfi 



lu some families the ditiiculty of classification was considi'iablc, and 

 a satisfactory method of dealing with a quantitative and variable char- 

 acter such as the present has yet to be discovered. In some few cases 

 only the quantity of pollen was recorded but as a rule both quantity 

 and quality were estimated on three or four different dates; especially 

 was this so when flowering was continued over a long period (this varied 

 in different seedlings from one to over fourteen weeks). 



Frequently the repeated observations both of quantity and quality 

 of ))()ilen agreed closely in different flowers on the same plant but in 

 some cases this was not so. Little is known of the factors causing such 

 variations. The variation of quantity is chiefly to be ob.^erved in sterile 

 or partially fertile plants, and may he, in part, a result of the irregular 

 and delayed ripening of the anthers cliaracteristic of such ])laiits. We 

 iiud the quality of pollen sometinu's deteriorates considerably after the 

 flower has been open for five or si.\ days, but apart from that there are 

 inherent differences in the degree of fertility. For instance, Edgecote 

 Purple invariably shows abundant pollen of high quality and may be 

 termed fully fertile. Edzell Blue on the other hand is somewhat variable 

 in quantity, usually only "medium" and the quality is correspondingly 

 inferior. 



We have not attempted to measure small (|uantitative differences 

 but only lai'ge differences of a more obvious kind. The methods of esti- 

 mation are, of course, appro.ximate and not suitable for accurate measure- 

 ment, but are sufficiently effective in determining large differences. 

 Rapidity of execution is also a ('onsideration when over three hundred 

 microscopic examinations need to be made in the flowerinu' ])eriod. 



Material u.sed. 



Three cultivated varieties formed the basis of the breeding experi- 

 ments. They are characf erised as follows : 



( 1) E (I f/ecote Purple. The male organs are I'lillv fertile. Imvinu a.hnndant 

 pollen of good quality of which at least 'J5 per cent, consists of ]ierfect 

 grains. It forms berries and seed freely by luitural self-pollination. Our 

 stock of this was brought by Professor Biffen Ironi \Viit>liii-c. where it 

 maintains a. fairly high yield although grown year aftei' year withoni 

 the usual renewal by means of Scotch or other seed. 



(2) Myatt's Ashleaf. The male organs are fully fertile like the pre- 

 ceding. It likewise forms berries and .seed, self-setting freely. 



(3) Edzell Blue. The male organs are fertile but not fully so, being 

 considerably less fertile than either of the two preceding varieties. Both 



