66 SCIENCE PROGRESS. 



immediately after its first formation, by the leaves in which 

 it is formed also appears certain. When plants whose 

 leaves contain it are put for some days in the dark the acid 

 gradually disappears, and as usual in such cases their whole 

 metabolism suffers. On being again illuminated the vital 

 processes gradually resume their activity. If a plant be 

 put in the dark till nearly all the acid has gone from 

 the leaves and then it be brought into the light, the little 

 that remains is soon removed by the returning activity of 

 the metabolism. 



That the acid is used, and not simply transported from 

 the leaves, can be shown in another way, by cutting a 

 circular section through the conducting tissue of the petioles, 

 when removal by transport becomes impossible. Yet the 

 hydrocyanic acid disappears gradually. 



It was said above that in some cases the hydrocyanic 

 acid itself might be looked upon as a reserve material. 

 This seems to be the case in the special cells described by 

 Treub in the cortex of plants when they do not contain 

 also proteid. In such cases we seem to have temporary 

 reservoirs to supply local and transitory needs and to 

 supplement the current passing along the bast. " Dans 

 les endroits non on pas suffisamment desservir pour le 

 systeme conducteur liberien ces usines locales prennent 

 naissance, et en plus grand nombre, a mesure que la 

 plante a on aura besoin dans ces endroits de plus de 

 substances plastiques." Thus in the older part of the 

 stem, where the active life is confined almost altogether 

 to the cortex, the latter contains many of these special cells, 

 while they are absent from the rest of the fundamental 

 tissue. Where they are present, as in certain portions of 

 the petioles, active life continues, although it may be de- 

 cadent in other parts. 



This temporary storage comes out very prominently in 

 the cases of the developing fruit and seed. At the base of 

 the former, just above its point of junction with the pedicel, 

 there is a very marked accumulation of the hydrocyanic acid, 

 the cells staining blue under the treatment described being 

 much more numerous than lower down the stalk. The 



