289 



Petit Thouars. He thought it was evident that whatevei' 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 

 woody fibres up to the leaf did not prove their origin there. With 

 regard to the descent of the sap, he did not agree with the author of 

 the paper, who, he thought, took too physical a view of the function 

 of the plant. The leaves were not mere organs of evaporation. 

 They performed the function of exhalation, which was independent 

 of heat, and depended on the vitality of the plant. He believed 

 that the leaves did effect a certain change in the juices brought 

 to them, which changed matter was again taken back into the sys- 

 tem of the plant, and there, being taken up by the cells, produced 

 the results which were found in the deposit of lignine and the other 

 secreted matters of plants. 



Mr. Huxley quoted the instance of the rapid growth and great 

 quantity of wood formed by the various kinds of Liana of tropical 

 forests as instances in favour of the formation of wood independently 

 of the leaves. These plants had all of them a remarkably small num- 

 ber of leaves. 



Prof. Asa Gray believed that the theory of the formation of wood, 

 as held by Du Hamel, Du Petit Thouars, and others, was no longer 

 tenable. The formation of vessels from cells could be easily observed, 

 and in exogenous plants there was no vacuity between the wood and 

 the bark for the woody fibres to be sent down through. Even in the 

 spring of the year, when the sap was passing most rapidly between 

 the wood and the bark, the organic connexion was complete. Whe- 

 ther matter was elaborated in the leaves and sent down into the plant 

 he was not prepared to say, but further experiments were desirable. 



Dr. Fowler quoted some ex))eriments which he thought proved that 

 the materials of the growth of the plant were not prepared in the leaves. 



Dr. Lankester replied, and stated that at present it appeared to 

 him that the statement of the preparation of gum or any other secre- 

 tion in the plant which was found subsequently in any other part of 

 the plant, was an assumption that required proof, and that all the 

 phenomena of vegetation were susceptible of a simple explanation, 



' Remarks on the Vitality of Seeds ; by Prof. Henslow.' The au- 

 thor stated that during the last year he had planted several seeds sent 

 to the Committee appointed to report on this subject, and out of those 

 he had planted two had grown. They both belonged to the order 

 Leguminosae, and one was produced from seed seventeen, and the 

 other from seed twenty years old. On the whole, it appeared that the 

 Vol. IV. 2 p 



