1906.] Plants on a Photographic Plate in the Dark. 387 



Usher and Priestley,* that formaldehyde and hydrogen peroxide are the first 

 products of growth, this action on a photographic plate is exactly what would- 

 occur. At the same time it must he remembered that terpenes and resins, 

 which are so commonly present in plants, can even in very small quantities, 

 either directly or indirectly, give rise to this body. 



Nuts such as walnut, Brazil nut, Barcelona nut, etc., act like seeds ; the 

 endosperm is inactive in its original state, but if charged, as nuts often are, 

 with a considerable amount of oil, this, on exposure to the air, oxidises and 

 becomes very active. For instance, if the kernel of a Brazil, Barcelona, 

 walnut, or almond nut be taken out of its shell and at once crushed between 

 blotting paper, neither nut nor expressed liquid are active, but if the paper 

 with the expressed liquid in it be kept for a short time exposed to the air 

 then it gives a very dark picture. If the nut be extracted with ether and 

 the solution evaporated, the residue becomes strongly active. Of all nuts and 

 seeds examined, castor-oil seed appears to be by far the least active ; the 

 expressed liquid from it may be exposed for a month or more, and it is still 

 without the power of acting on a plate. 



The examination of different bulbs has shown that the fleshy scales 

 forming them, from centre to outside, are active, but that the nucleus of the 

 future plant which it contains, if in its primary state, is inactive like the 

 plumule in a seed, but when growth has commenced it is active. This is 

 well seen in the snowdrop, onion, and shallot ; the shoot, if not visibly 

 grown, is quite inactive. The amount of activity of different bulbs varies 

 very considerably : the snowdrop bulb is slightly active, whereas the narcissus 

 and the tulip bulb is much more so. This variation may probably depend to 

 a considerable extent upon the state of development of the bulb. In the 

 case of the crocus, which has a solid bulb, its activity is like those above 

 mentioned. The tuber of the potato squeezed between blotting paper gives 

 a very active jiiice, the Jerusalem artichoke a juice which is much less 

 active. If bulbs or tubers be dried even at ordinary temperatures they lose 

 their activity. The rhizome in different plants varies much in its activity, 

 and probably in the same plant at different times of the year ; in the iris it is 

 but very slightly active, in sea kale it is more so, and in the Pteris it is very 

 active. 



A considerable number of different roots have been experimented with, 

 and in all cases it has been found that the root has very considerable 

 activity ; in fact, the root of some of the larger trees — for instance, Scotch fir — 

 gives a picture similar to that given by the wood itself. 



There are some interesting points with regard to the shells which protect 

 * ' Roy. Soc. Proc.,' B, vol. 77, p. 369. 



