278 BRIEF REMARKS. 



in the whole year, if the winter is very mild, is the best month for some 

 particular tlant to be removed, and that I, and the whole of us, 

 were quite wrong in supposing the autumn, or any particular time, to 

 be the best time for all evergreens to be removed. "We might just as 

 well have broached a new doctrine about potting every plant we grow, 

 bulbs, orchids, and all, in one month, as to assert that one particular 

 month in the autumn, or spring, or summer is the best time for all 

 evergreens to be moved ; but let us have more observations than mine 

 recorded on the subject. — D. Beaton. ( Cottage Gardener, .) 



British Association for the Advancement of Science. — On 

 the Theory of the Formation of Wood and the Descent of the Sap in 

 Plants, by Dr. Lanhester. — The author drew attention to the theory 

 of the formation of wood in plants, and objected to the view that the 

 leaves form the wood, on the ground that the ligneous, like all other 

 tissues, were the result of the growth of cells which were not formed in 

 the leaves, but in all parts of the plant. Wood was formed in all parts 

 of the plant where elongated cells were generated, quite independently 

 of leaves, or the formation of leaves ; as in the lower part of the cut 

 wounds of the stems of plants, in the portions of trunks left when trees 

 were cut down, in the abortive branches formed in the bark of such 

 trees as the Elm and the Cedar, and in other parts of the vegetable 

 structure. He also objected to the theory of the formation of the 

 ligneous or any other secretion, which might be subsequently appro- 

 priated by the cells, in the leaves alone. He maintained that all the 

 facts brought forward to support the theory of the descent of the sap 

 might be explained on the known fact of the ready permeability of the 

 tissues of the plant. He related the details of experiments performed 

 on the species of Spurge, in which the fluid was found to exude from 

 the stem and branches in these plants just in proportion of the quantity 

 of fluid contained in the plant above or below the section made, and 

 not in obedience to any law of the descent of the sap. The cells of 

 plants were nourished in two ways : first, by the sap containing car- 

 bonic acid, ammonia, and other substances ; and, secondly, by materials, 

 as sugar, gum, &c, formed in the cells. These latter were not formed 

 solely in the leaves, but in all cells. He regarded the leaves as organs 

 by which the water of the sap was got rid of, and by this means a 

 further supply of sap from the earth and atmosphere was insured. The 

 way in which the demand for sap was insured might be imitated by a 

 common sponge, on the upper surface of which evaporation went on, 

 and the lower surface, being in contact with water, would always supply 

 this fluid, as a demand for it was created by the evaporation above. 

 This phenomenon had been attributed to a specific vitality ; but it was 

 unphilosophical to speak of vitality as a force, when it could not be 

 demonstrated to exist, and especially when physical forces were capable 

 of explaining the phenomenon. 



Professor Henslow said that he agreed with the views of Dr. Lan- 

 kester with regard to the theory of the formation of wood proposed by 

 Dupetit Thouars. He thought it was evident that whatever was the 

 function of the leaf, it did not send down the woody fibres which 

 formed the trunk and branches of exogenous trees. The tracing the 



