24 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



In recapitulation it is to be said that the auxographic record of 

 a plant is a resultant of its reversible and irreversible changes in 

 form. 



The permanent changes in the cactus dependent largely on its 

 type of respiration take place in the day time when the accumu- 

 lated acids are disintegrated by the action of light, and growth 

 continues at the expense of the available sugars until the balance 

 or supply is reduced to a minimum. Reversible changes in form 

 rest upon water-holding capacity and the distensive action of 

 osmotic and hydration pressure. Temporary enlargements cumu- 

 late with decreasing acidity and decreases or shrinkages follow 

 falling temperatures and heightened acidity, being coincident in 

 some cases with maximum transpiration. With this interpreta- 

 tion of the auxographic record accepted, it is now possible to pro- 

 ceed with a general summary of the relation of temperature and 

 light to the processes under discussion. The facts already pre- 

 sented tend to show that temperature influences the diffusion of 

 food-material at a low simple ratio, that food-formation, hydro- 

 lysis, and the formation of building material take place under 

 van't Hoff's law, and as temperature also affects osmotic pressure, 

 permeability, and hydratation capacity, it is the dominating 

 agency in determining the course, rate, and consequently the 

 final amount of growth. It may have supra-optimal, as well as 

 minimum effects. 



Light, especially the shorter wave-lengths, exerts a neutralizing 

 or coagulatory action on many of the colloids of the protoplast, 

 but as such radiations have the least penetrating power, this 

 action is most marked in the minute organisms, or in those with 

 translucent membranes or outer integuments. It is in accord 

 with these facts that the action of enzymes may be retarded by 

 light of certain wave-length and intensity, and also that stems 

 devel()i)ing in thr illuniinatioii of a nuTcury \'apor arc lain]) sliow 

 grotesfiue deixirturcs from the normal form. Tiiere seems to be 

 a marked specificity of the wave-length upon the relatixe develop- 

 ment of various tracts, but these morphogenic effects may be 

 dealt with in another paper. How far "permeability" as de- 

 pendent upon the relations of disperse phase and disperse medium 

 of protoplasm may be affected by light is not yet clear. It is 

 clear hovve\'er that the disintegration of clogging or smothering 



