DANIEL S EXPERIMENTS AND CONCLUSIONS I7I 



218. Reasons for the above effects. — The theory by wliicli Dniiiel 

 seeks to explain these facts is in brief as follows : The nntrition 

 of stock and cion is modified by two causes which may act in the 

 same or contrary directions. These are (1) the callus consequent 

 on the operation, and (2) the difference between the peculiar func- 

 tional capacities of stock and cion, such as differences in structure, 

 special diastases, differences in composition of the crude or the 

 elaborated saps, etc. The phenomena produced are dependent, not 

 only on the nature of the plant, but intimately so on environment. 



From this theory certain conditions of success in grafting may 

 be deduced. The protoplasm of stock and cion must not, as a 

 result of the operation, be modified beyond that definite point at 

 which poisoning sets in or at which the essential properties of the 

 living substance, as nutrition and motility, are destroyed. De- 

 struction of the protoplasm may result from either of two causes : 

 (1) action of plastic or waste products brought together suddenly, 

 causing immediate poisoning or gradually causing slow poisoning. 

 These products may give rise through mutual reactions to other 

 injurious products. (2) Deficiency or excess of water in stock 

 or cion consequent upon grafting. 



Daniel demonstrates the insufficiency of the hypothesis of 

 relationship and that of similarity in composition of elaborated saps 

 to account for the success of a graft or to explain its variations. 

 He reports a large number of experiments, each illustrating a dif- 

 ferent variation, produced directly by a mutual reaction of stock 

 and cion. Specific variations differ much in degrees according to 

 the nature of the plant and even according to the part of the 

 cion. The principle applies alike to herbaceous and woody plants. 

 Specific variations result in a more or less complete blending of 

 the characters of stock and cion ; or more strictly, these char- 

 acters appear side by side but separate and distinct. 



219. Geotropism, the tendency of plant parts to grow 

 downward toward the center of the earth, as in ordinary 

 roots. Negative geotropism (apogeotropism) is the 

 growing away from the earth, as in ordinary stems. 



220. Transmission of grafted cHaracters by seed. — From certain 

 experiments Daniel concludes that variations due to nutrition are 

 in some cases transmitted by seed collected from the cion, even 

 when no morphological changes are apparent in the cion itself. 

 Such cases show that the immediate influence of stock on cion may 

 be less than the indirect influence of the offspring of the cion. 

 Seed grafts of wild carrot on the cultivated half-long red variety 

 showed clearly such a mixture of the characters of stock and 

 cion that the resulting plants might be considered true crosses or 

 graft hybrids produced by the influence of stock on embryo. 

 These and similar experiments show also that by grafting a wild 

 and a cultivated plant the former may be made to acquire definite 

 qualities which can be improved by selection. Experiments showed 



