240 Transactions of the Royal Canadian Institute 



(MacDougal, '16; MacDougal and Spoehr, '17) should be mentioned 

 here. In this form, the total behaviour in respect of growth is precisely 

 the reverse of that in Eriogonum. These two types indeed exemplify 

 two physiologically widely different kinds of plants, which however are 

 not coextensive with succulency and non-succulency. Opuntia contains 

 pentosan emulsoids in large amounts (Spoehr, '19, Lloyd, '19, Stewart, 

 '19) in high concentration, and may therefor be assumed to be capable 

 of displaying imbibition pressures sufficient to account for measurable 

 changes of volume of the plant body, according to the varying con- 

 ditions of acidity. 



The march of growth is such that acceleration takes place during 

 the hours from sunrise till noon, "parallel to the disintegration of the 

 clogging acids and the rising capacity for imbibition" (MacDougal and 

 Spoehr, '17, p. 310). The cessation of growth after the noon hour calls 

 for other as yet undetermined factors, since the "water holding capacity 

 of the tissues is highest when the acidity is lowest" (E. B. Shreve, '16) 

 and this occurs in the late afternoon (Richards, '15 ; Long, '15) : and since 

 transpiration is low throughout the day (Livingston, '06) and the sto- 

 mata are closed (Shreve, i, c.) 



From the present account we have seen that Eriogonum presents a 

 far different picture. In this the cells of the growing region are delicate 

 protoplasmic utricles, with thin cell-walls, and the emulsoids of the 

 vacuolar sap are present only in very low concentration, and would 

 therefore be capable of exerting but limited pressures as compared with 

 the osmotic pressures due to the presence of salts, sugars, etc. A tissue 

 composed of such cells is chiefly an osmotic mechanism, and osmotic 

 pressures must be regarded as of first importance in premitting and 

 maintaining growth rates. It is the same sort of mechanism as occurs 

 in the roots of Helianthus, in the submersed roots of which Borowikow 

 ('13) however, found growth to be influenced by the alterations in the 

 hydratation capacity of the emulsoids. The same might be postulated 

 of Eriogonum, but for the apparent absence of evidence of suitable acid 

 concentrations, and of the necessary changes in them. Professor H. M. 

 Richards found the acid content of Eriogonum collected from plants, 

 growing in 191 8 in the same spot as those on which my studies were 

 made, to be, per gram of fresh material in terms of N/20 alkali, 4.75 c.c. 

 at 9 hour, 4.90 c.c. at 15 hour and 4.70 c.c. at 18 hour. 



Until we know more about the physiology of this plant, it is un- 

 profitable to speculate on the possibilities from this point of view. We 

 know, however (Lloyd, '17, '18) that protoplasm as an emulsoid complex 

 is extremely sensitive to minor changes in acid and alkali concentration, 

 and while some protoplasm will cease to function in the presence of 



