20 
may be evolved again, by the second parcel, on the other side. Certain plants 
may absorb some 4 poisons’ by their roots, with impunity, which would be destruc¬ 
tive to others. Other phenomena illustrate and confirm these truths, and it 
would be altogether superfluous to detail them. 
But irrespective of the facts connected with the excretions of the roots which 
have been assumed as explanatory of the necessity of the rotation of crops, there 
is another interesting question involved in the curious inquiry, to which I am 
desirous to call attention, and which, as far as I know, has never been once sus¬ 
pected. It is this : how far particular plants may, or may not, prove injurious by 
their proximity to others, from exudations and exhalations of a more or less vola¬ 
tile kind, as well as gaseous products arising from stems, foliage, and flowers ; and 
therefore to what extent plants reciprocally affect each other. Certain plants grow 
freely side by side, or in juxta-position; whilst the very reverse is the fact with 
others. Certain shrubs luxuriate beneath the shade of trees, and the copious 
showers that trickle from their branches; while myriads would be destroyed 
under similar circumstances. Many plants perish near others, or disappear 
without any visible cause. Though the corrosive liquid that distils from the 
branches of the Manchineel is of too palpable a character to be questioned, there 
are others that seem more dubious. The blighting influence of the Barberry on 
certain crops, however, appears not to be apocryphal. The hardiest weed will not 
dare to shew itself beside that gigantic reed, the Bamboo; and bees fall down 
dead suddenly, should they per<diance alight on the branches of the Rhus vernioc. 
J. MURRAY, F.L. & G.S. 
( To be continued.) 
AN ACCOUNT OF THE STRUCTURE OF THE HEART IN THE 
TESTUDO MYDAS, OR GREEN TURTLE. 
The heart, in the several families of the Tortoises and Turtles, presents 
curious peculiarities adapted to the mode of life of the animals in whom these ano¬ 
malies of anatomical disposition are met with. Each species varies a little in the 
anatomical structure of the central organ of the circulation; but I shall, in this 
paper, take the Testudo my das as the type of all animals of this order. The 
Testudo my das, or Green Turtle,—the Tortue franche, of Cuvier, called by the 
Germans, die Grime Schildkrote,—is found on all, or most of, the coasts of the 
torrid zone, feeding upon the weed at the bottom of the ocean, approaching the 
