28 BULLETIN llSiS, U. S. DEPARTMKNT OF AGRICULTURE. 



In physiological incompatibility, well exemplitied in the lilies, fruit and seed 

 production depends on the stimulus of compatible fertilizations, and the bulb 

 or tuber forming plant is consequently found to be fully capable of developing seeds 

 when the proper and compatible pollinations are made. 



(2) Experimental proof of a direct and simple competition for food between tubers 

 or bulbs and the forming seeds is lacking. The older statements frequently quoted 

 that the flowering branches of such plants as Lilmm candiduni and Hemerocallis fulva 

 will produce fruit and seeds only when they are cut and placed in water and that 

 the removal of aerial bulbleta from such plants as Lilium tigrinum and Ficaria ficaria 

 will lead to seed formation are incorrect. This matter has been tested carefully in 

 experiments at the New York Botanical Garden with results showing that when pods 

 are produced in such cases the plants are to some degree self-compatible and able to 

 produce pods on branches left attached, provided the same care is taken in making 

 the pollinations. 



Experiments with the potato which attempt to test for correlative sterility have 

 all given negative results, at least since the favorable results reported by Knight {14y 

 p. 58). In an experiment of this sort East {4, p- 432-433) prevented the formation 

 of tubers in plants of the three varieties Rural New Yorker No. 2, Green Mountain, 

 and Irish Lemon. In comparing treated with untreated plants he found no increase 

 of apparently good pollen, and to pollinations of 50 plants of each he obtained 6, 9, 

 and 2 fruits, respectively, for the treated, and 4, 8, and 4 fruits for the untreated. 

 The marked fruitlessness of these varieties to self-pollination was not changed by 

 this treatment. 



It would seem that a critical experimental test of a direct correlative sterility in 

 potatoes could be made by gi-afting branches on species of Solanum that do not form 

 tubers. A few years ago an extensive experiment of this sort was conducted by 

 Prof. C. H. Myers and an assistant, W. I. Fisher, at the Agricultural Experiment 

 Station of Cornell University. The results have not been published, but a copy of 

 the report has been kindly furnished by Professor Myers to the writers. Branches 

 of 16 varieties were grafted on various species of Solanum which do not form tubers. 

 The varieties thus used were Beauty of Hebron, Blue Victor, Carman No. 3, Early 

 Ohio, Early Rose, Green Mountain, King Edward VII, Moravia, Pat's Choice, Phoe- 

 bus, Rural New Yorker, Sir Walter Raleigh, State of Maine, Vermont Gold Coin^ 

 Wohltmann, and an unknown sort. Most of the grafts were made on Solanum ciiiatum, 

 S. sysimbrifolium, S. miniatum, and S. nigrum. In all, 200 successful grafts were 

 made, and the plants were grown to good maturity out of doors in a garden. Many 

 careful hand pollinations (evidently self) were made on flowers, but only one seed 

 ball was obtained from the whole lot. In these grafted plants there was no tuber 

 formation to draw food from the aerial parts. The results are positive in indicating 

 that fruitfulness in these plants is not increased when the qualitative competition 

 for food between vegetative organs and organs of seed production is removed. The 

 sterilities to own pollen, here due in large part to impotence of pollen, or also to ab- 

 scission were not removed by such experimental methods. There was no indication 

 in the results that the nature of the flowers and of their sex organs was influenced 

 or changed. 



(3) In a careful study of the osmotic pressures in potato plants with reference to- 

 the distribution of food at various stages of growth Lutman {15) has shown that while 

 a superior osmotic pressure seems to be necessary for the formation and growth of 

 new sprouts the growth of berries (fruits) and of tubers can not be thus accounted 

 for, since the osmotic pressures in these organs are the least of any in the plant. Lut- 

 man points out that there appears to be a pumping action of the sieve tubes, but 

 that a study of the comparative osmotic pressures does not reveal the manner in 

 which they may induce the observed flow of food materials even to the tubers. 



(4) F'or the cultivated varieties of the potato the evidence is clear that when con- 

 ditions favor blooming the use of viable pollen gives fruit in abundance. FVuit is 

 often abundantly found in the Held, especially on varieties having considerable good 

 pollen. Furthermore, a study of the comparative yields of tubers and seed balls for 

 plants of such a variety (Lookout Mountain or McCormick) by Newman and Leonian 

 {l7, p. 14) has .shown that "in most cases the heaviest tuber jjrodurtion, the richest 

 vegetative growth, and the largest seed productions go hand in hand." There are, 

 however, v.vrioiis conditions inliuenciiig the growth of plants, tlie yield of tul)er8, 

 and the production of seed balls. Under certain of these conditions there may be 

 internal regulation of development that directly or indirectly determines whether 

 the HUccps.s or failure of the stimulation of fertilization is to bo etfective. 



The main point of the evidence noted above re^ardinj^ the setting; of 

 seed is that under favorable conditions for bloomino;, potatoes are welK 



