169 



Johannsen showed, as we have already noticed (See page 29) that modifi- 

 cations within a "pure line " are not transmissible and therefore cannot be 

 utilized in the improvement of the race. Since reproduc^n in potatoes by 

 means of tubers is really reproduction in a pure line it would seem that no 

 improvement is possible even in this crop by the selection of "plus" fluctua- 

 tions. That improvement in potatoes has actually been made at Svalof by 

 a careful selection of tubers seems fairly well established, although there has 

 not yet been sufficient time to show absolutely whether or not these apparent 

 advances in all cases are real or imaginary. If real, they may be due to some 

 sort of mutation, as changes belonging to this category are believed to take 

 place in such vegetative parts.* On the other hand, they may be only 

 imaginary since the enormous effects of climate, soil and season may have 

 so confused the results as to make it appear as though progress had actually 

 been made. 



Correct conclusions are possible only after properly controlled experi- 

 ments. In order to throw more light on this problem of variation as it 

 affects vegetative parts, material for investigation was obtained at Svalof 

 from the sort No. 1041. This sort gave a very satisfactory yield with an 

 average per cent of starch. The tubers were oval but somewhat irregular 

 with large eyes of medium depth and with fine netted skin. The color was 

 blue-violet or almost black. In 1905, eight tubers from the above sort were 

 planted. These gave well developed plants which showed some slight differ- 

 ences in the character of the leaves. Three of these deviating plants were 

 marked and harvested separately, the hills being labelled a, 6, and c. These 

 were preserved and used the following year.. to plant three separate plots. 

 An examination of these plots showed that the peculiarities of the mother 

 plants had been quite accurately reproduced in each case. An examination 

 and analysis of the tubers from each plot was made and served to further 

 establish well defined differences. The flesh of c was a deep violet, while that 

 of b was only faintly colored. The starch content of c was 17.1%, but with a 

 and 6 reached 17.7%. The yield of c was only 25,200 kg. per hectare while 

 that of a was 29,160 and that of b 33,120. In the following year (1907) these 

 relative differences were maintained, c giving 13,680 kg. and 15.4% starch, 

 a giving 18,000 kg. and 16.3% starch and 6 giving 21,240 kg. and 16.4% 

 starch. 



In 1908 a further comparison was made but this time at two different 

 centres, viz., Svalof and Bdketofta. The results of this test are recorded as 

 follow (24, p. 214) : 



(Svalof). (Boketofta). 



(a) 23,580 kg. and 16.5% starch. 21,600 kg. and 16% starch. 



(b) 22,680 " 16.4% " 19,980 " 15.7% 



(c) 14,440 " 13.8% " 13,320 " 13.5% 



* Numerous examples are cited by different investigators, of the production of new sorts by means of 

 changes which are supposed to have been of a mutative character. In Fiihlings Land'w, Zeitung, 1910, 

 No. 16, p. 537, for example, an account is given of the production by Von Lochow of a number of sorts 

 by the selection of such variations found in the well known sort Wohltmann. 



