276 



HARDWICKKS SCIENCE-GOSSIP. 



These are the principal species recognised. There 

 is another kind less esteemed imported from Aleppo, 

 consisting of the leaflets of C. obovata, but this kind 

 is subject to great adulteration, and is not recognised 

 by the " British Pharmacopoeia," although it is largely 

 used, as well as the leaflets of C. acutifolia, for the 

 adulteration of the finest kind. The leaves of other 

 plants are often used for the adulteration of senna, 



I <; 



Figs. 149. — Senna Leaves, a, Cassia elongata; b, C. obevata ; 

 c, C. acutifolia. 



but true cassia leaves may be easily recognised by 

 being unequally-sided. 



The nauseous taste and smell of senna is due to 

 the presence of a volatile oil, stored up in reservoirs 

 in the leaf-tissues, while the purgative effects are 

 produced by a chemical substance known as " cathar- 

 tin," according to some authorities. 



All the species mentioned here are grown at the 

 different botanic gardens in this country. C. acuti- 

 folia and C. obovata are figured in "Nees Plant. 

 Med.," PI. 345, 348. C. elongata is figured in 

 Royle's "Bot. Himal," PI. 37. 



Although, as mentioned above, it has been stated 

 that the purgative properties are due to the presence 

 of "cathartin," it is well to remember that others 

 have disputed that statement, notably Mr. Heberlein, 

 whose experiments seem quite sufficient to prove 

 that the active purgative properties do not exist in 

 the cathartine contained in the leaves. 



J. T. Riches. 



THE EVOLUTION OF POISONS IN 

 PLANTS. 



IT is generally admitted that the development of 

 poisonous constituents in plants is in its object 

 defensive. The more wholesome any plant, the 

 greater, on the principle of natural selection, should 

 be its chance of escaping destruction by animals, and 

 consequently of survival and extension. But in 

 numbers of cases poison seems to afford no pro- 

 tection. Every one is aware of the noxious character 

 of the common foxglove ; but to certain animal 



species, and especially to those most important to be 

 repelled, the poison is harmless, if not attractive. 

 A slug or a snail will feed in a plot of seedling fox- 

 gloves just as will a donkey in a carrot field, or a 

 cow in clover, not for want of more suitable food, 

 but preferentially, passing over harmless plants. So 

 that the poison of the foxglove as a protective agent 

 is a complete failure. 



The laburnum tree when young is very liable to 

 the attacks of the same depredators, which may 

 often be picked off its lower shoots, and its bark 

 does not escape the unpleasant attentions of rodent 

 mammals. The bark of the mezereum is rich in an 

 irritant poison, but hares and rabbits gnaw it greedily 

 in the winter season, and often completely spoil the 

 trees. 



The periwinkle, as it is absurdly called, in con- 

 sequence of successive corruptions, is greedily con- 

 sumed by snails and slugs in spite of its dangerous 

 properties. 



As to insects, they seem to frequent and feed upon 

 poisonous plants quite as eagerly and commonly as 

 upon wholesome species. As a few instances, we 

 may take the oleander hawk, which preys on the 

 leaves of the oleander and the periwinkle, both 

 poisonous ; the " death's head" {Acherontia atropos), 

 which feasts with impunity on the deadly night-shade 

 {Atropa belladomia) ; the spurge-hawk (Deilopkila 

 euphorbia), as well as Ckelonia kebc, and Calocasspa 

 exodata, have for their regular diet various species of 

 the spurge plant. No plant is, I think, more zealously 

 devoured, both by insects and snails, &c, than the 

 common night-shade and bitter-sweet. 



We see, therefore, that poisons fail to protect 

 plants against some of their worst, we might say 

 their very worst enemies, i.e., snails, slugs, and the 

 bark-eating rodents. If, then, their production de- 

 mands a certain expenditure of vital energy, we may 

 venture to say that poisonous plants are in a worse 

 position than their harmless neighbours, and we have 

 still to ask — wherefore, then, the poison ? 



J. W. Slater. 



THE SMALL-END COLOURING OF EGGS. 



WITH reference to Mr. Wheldon's note on this 

 subject in February, and to Mr. Nunn's in 

 Science-Gossip for October, I should like to state 

 the result of my experience, which goes to show that 

 examples of small-end coloured eggs amongst sea 

 birds is very rare indeed ; in fact, I may add that 

 out of some three hundred very choice varieties of 

 eggs of the guillemot in my collection, selected from 

 several thousands, I can only find one so marked, 

 and don't remember having ever seen another. The 

 variety in question is of a pale uniform white colour, 

 with a rich deep brown circle at the lower end. 



Out of some eighty fine varieties of the eggs of the 

 razorbill, I fail to find one single example thus 



