450 Brenchley. — Organic Plant Poisons. I. 
t. That it is a waste product of no metabolic importance. 
2 . That it is a means of protection against marauders. 
3. That it is an intermediate product in the synthesis of proteids, 
a view to which Henry 1 himself is favourable. 
Though Treub’s idea as to the function of hydrocyanic acid in meta- 
bolism received support from many other investigators, Guerin raised con- 
siderable opposition to it. Guerin 2 held that the relative rarity of hydro- 
cyanic acid in plants constituted a serious objection to the adoption of the 
hypothesis that it is one of the materials at whose expense nitrogenous 
matters are elaborated. He felt that this hypothesis, which admits that 
HCN constitutes the first product of assimilation in green plants, does not 
meet, in every case, objections from the chemical point of view ; that, while 
admitting that in certain cases HCN serves for the building up of albu- 
minoid matters, one must also admit that its role completely escapes one 
when it is found engaged in those complex molecules which constitute the 
glucosides. The leaves of elder and passion flowers, at the time of their 
fall, contain as much cyanogenetic glucoside as during the preceding months, 
so that it is very difficult to attribute to this body the role of a reserve 
material. Also, it is still less satisfactory to see in these compounds a pro- 
tective substance against the attacks of animals and insects. Altogether 
Guerin maintained the incompleteness of our knowledge as to the role 
of hydrocyanic acid in plants, and emphasized the need for further 
investigation in order to solve the problem, which is one of great importance 
in vegetable biology. 
In view of Treub’s suggestion as to the part played by HCN in plant 
nutrition a few experiments have been made on the action of HCN when 
supplied to plants from the outside. It is evident that while certain (and 
perhaps most) plants can elaborate some amount of HCN within their 
tissues, yet this same substance is most toxic in nature when offered 
from outside. Townsend 3 tested the effect of hydrocyanic acid gas upon 
grains and other seeds under different conditions. He found that dry seeds 
are very resistant to the action of the gas — that short exposures do not 
affect germination at all, and that exposure for several months to gas 
generated from 1 grm. KCN per cubic foot of air does not altogether 
destroy the power of germination. Damp seeds, however, are far more 
affected, the length of soaking determining the reaction to the hydrocyanic 
acid gas. HCN is also capable of holding the germination of soaked seeds 
in abeyance for some considerable time without destroying their vitality 
even when other conditions are favourable to growth. 
1 Henry, T. A. : Sci. Prog., vol. i, 1906, pp. 39-50. 
2 Guerin, P. : Revue Scient., vol. viii, 1907, pp. 65-74, 106-10, 
3 Townsend, C. O. : Bot. Gaz., vol. xxxi, 1901, pp. 241-64. 
