Growth in Eriogonum nudum 239 



the daytime. And A. M, Smith came to a similar view, viz., that in 

 Dendrocalamus "two factors of the physical environment in turn limited 

 the rate of growth of the culms (i) the temperature of the culm and 

 (2) the supply of water to the culm. The second factor being intimately 

 connected with the amount of water drawn off by the transpiration of 

 the adult culms on the same rhizome, depends in its turn on two factors: 

 (i) the humidity of the atmosphere, (2) the intensity of the light". 

 Further, "the cases of the runner shoots of Capparis and Stiff tia are 

 explicable on the hypothesis that the supply of water is the limiting 

 factor by day and the temperature by night. No decisive case of retard- 

 ing light effect was obtained". 



The influence of increasing humidity conditions in accelerating 

 growth in the fleshy fruits of Ly coper sicum has also been recognized by 

 MacDougal ('19). The cessation of growth, or shrinkage, following on 

 conditions leading to excessive transpirational loss, as occurs in the early 

 portion of the forenoon in Eriogonum, adds another instance to an already 

 long list of plants in which the same has been observed, e.g., Gossypium 

 (W. L. Balls, '12, Lloyd, '13), Helianthus (Balls, '12, MacDougal '18), 

 to cite more recent results,^ to which may be added the cases of net water 

 loss in leaves measured by Livingston and Brown (12) and by myself 

 ('12, '13, '20). 



It is evidently felt and tacitly if not expressly admitted by some of 

 the above quoted authorities that a small light effect may be present 

 but, because of the masking effect of other factors, is not obvious enough 

 for measurement under the conditions of field study. The accurate 

 studies of Blaauw ('14) on Phycomyces and Helianthus would seem to 

 justify this, for he found a temporary depressing effect of light when 

 first admitted on Phycomyces, followed by a temporary excitation; and 

 the reverse on Helianthus. Blaauw, however, specifically contests and 

 controverts the classical error of the supposed inhibition of growth by 

 light as formulated by Pfeffer from the work of Vines and others then 

 available, and it is largely to the same end that the study here recorded 

 was undertaken. 



Release from this mistaken conception, recognized as such by Mac- 

 Dougal ('03, '15) in 1903, has gone hand in hand with those studies on 

 growth which latterly directed attention to the role of colloids (emul- 

 soids). Of comparative interest in- the present connection are the results 

 attained by MacDougal, MacDougal and Spoehr, E. B. Shreve, Boro- 

 wikow, Lloyd and others^. In particular the behaviour of Opuntia 



^ For others see papers of Lock and of Smith. 



* Additional pertinent literature will be found cited in those papers of these authors, 

 mentioned in the list accompany the present paper. 



