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cells of the flesh. Mr. Gosse drew analogies to illustrate this 

 structure from the Medusa), the Hydrae, and especially from the 

 Spirostoma and the Stylonychia, polygastric animalcules ; and his 

 observations went to show that the organization in this class of 

 animals is exceedingly simple, consisting of little more than a homo- 

 geneous fluid drawn out into spherical films or cells, probably 

 inclosing a very subtle vapour. 



A second paper, by H. C. Sorby, Esq., * On the Tensions developed 

 among the Tissues of Wood by its Growth,' was read. 



The author commenced by stating that in studying the depolarizing 

 structure of wood, he had used as a polarizer a rotatable large 

 Nichol's prism, placed behind the lenses of the achromatic condenser; 

 and as an analyzer, a film of selenite and another Nichol's prism, 

 which could be rotated independently or conjointly, placed over the 

 eye-piece. By these arrangements, he obtained abundance of light 

 when using high powers ; and by rotating the selenite, the direction 

 of the positively and negatively doubly-refracting axes of the object 

 under examination were easily ascertained. 



Upon examining with this apparatus longitudinal sections of recent 

 wood, with a power of about 400 linear, they were found to consist 

 of laminae, some of which possess positive and others negative double 

 refiaction in the line of their length, the principal axes lying one in 

 that direction and the other at right angles to it. This alternation of 

 positive and negative laminae, and the probable cause, form the prin- 

 cipal subjects of this paper. The number of alternations varies, but 

 from five to ten are usual. The passage from one to the other is 

 often quite sudden, but is sometimes gradual. The wood considered 

 as the best for showing these effects was that of the Coniferae ; and 

 the effects of polarization, as exhibited by the medullary rays, the 

 disks, the spiral fibre, and the ducts were described. The cause of 

 alternation of the positive and negative laminae is ascribed by Mr. 

 Sorby to the tension produced by the growth of the plant ; and he ex- 

 plains it by supposing that first of all the original walls of the tubes 

 of which the laminae are composed were neutral, or had such a variable, 

 slight, positive and negative action as is seen in cellular tissue, and 

 that then inside them woody matter was deposited, which had a ten- 

 dency to expand in the line of the length. This, by stretching the 

 original walls, would produce in them a positive action in the line of 

 their length, and their reaction on the fresh-formed tissue would de- 

 velop in it a negative structure ; and a constant repetition of this pro- 

 cess would produce the various alternations now under consideration. 

 Vol. IV. 2 h 



