338 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



One of Vochting's experiments 1 illustrates how this sort of operation may 

 furnish evidence concerning the chemical processes in plants. In this case the 

 leafy stem of a young sunflower plant {Helianthus annuus) was cut off a short 

 distance above the soil and to the cut surface of the stump was grafted a leafy 

 branch of the Jerusalem artichoke (Helianthus tuberosus). Union of the two 

 parts soon occurred and a new plant was formed. Examination of the sap 

 showed that the upper portion, down as far as the plane of the graft, contained 

 inulin in abundance, while the part below the plane of the graft contained starch 

 but no inulin. In this case the simple organic substances in the sap of both 



portions were produced in the artichoke leaves above. In 

 the reverse experiment, where the upper part was sunflower 

 and the lower Jerusalem artichoke, a similar result was 

 obtained; namely, that starch but no inulin was present in 

 the sunflower portion while the artichoke portion, which here 

 received its simple organic substances from the sunflower 

 leaves, contained an abundance of inulin and even bore 

 tubers, in which inulin accumulated in the same way as if 

 the whole plant had been of the artichoke species. Inulin 

 clearly acts only as a reserve carbohydrate. In both ex- 

 periments the products of photosynthesis were present in 

 both stem and roots as glucose, but within the limits of the 

 sunflower portion they accumulated as starch, while within 

 the limits of the artichoke portion they accumulated as 

 inulin. 



The operation of transplantation is successful only when 

 closely related species are involved, as may be understood 

 from the foregoing discussion (page 331) of hormones and 

 of the chemical differences between the metabolic sub- 

 stances of forms not closely related. 



Fig. 173. — Three 

 varieties of gourd 

 grafted upon one an- 

 other; a, a fruits jau- 

 nes; b, poire verte; c, 

 a fruits blancs. 



Summary 



1. Influence of External Conditions on Development. — 



The development of a plant is of course made up of all of its 

 growth activities considered together. The external or internal 

 conditions that influence growth also influence development. As the plant 

 develops, its internal conditions (its physiological characteristics) are continually 

 changing, the conditions of the natural surroundings are also always in a state of 

 fluctuation, and consequently the relations between internal and external conditions 

 are likewise continually varying. It is these relations that really deteimine the develop- 

 mental processes. With a given kind of internal complex, a certain set of environ- 

 mental conditions would produce a certain kind of growth if they allowed growth to 

 occur at all. If either the internal or external conditions were markedly different, the 

 kind of growth would be correspondingly different. Thus, different species in the same 

 environment develop differently, and different individuals of the same species, but in 



1 Vochting, H., Ueber die durch Pfropfen herbeigef iihrte Symbiose des Helianthus tuberosus und Heli- 

 anthus annuus. Sitzungsber. K. Preuss. Akad. Wiss. Berlin. 1894: 705-721. 1894. 



