311 



Since it seems thus established, that the foetus is nourished with- 

 out a placenta, the source of the gelatinous matter provided for its 

 nourishment becomes a natural object of inquiry. In birds the al- 

 bumen of the egg, which corresponds with this jelly, is formed in a 

 tube called the oviduct, and the lateral canals, which open into the 

 cavity of the uterus of the wombat and kanguroo near its neck, bear 

 a strong resemblance in their form to the oviducts of birds ; and in 

 the kanguroo they were found, in the impregnated state, to be en- 

 larged, and to have a very free communication with the uterus ; cir- 

 cumstances which induce the author to believe their sole use is to 

 form the jelly, and to deposit it in the uterus. 



On the Origin and Office of the Alburnum of Trees. In a Letter from 

 Thomas Andrew Knight, Esq. F.R.S. to the Right Hon. Sir Joseph 

 Banks, Bart. K.B. P.R.S. Read June 30, 1808. [Phil. Trans. 

 1808, p. 313.] 



Mr. Knight having, by his former experiments on this subject, 

 established to his satisfaction that the bark of trees is not converted 

 into alburnum, but that the albunious matter is deposited by a fluid 

 which descends from the leaves, and is subsequently secreted through 

 the bark, proceeds to inquire into the origin and office of the albur- 

 nous tubes. 



In the succulent shoot of the horse-chestnut it may be seen, that 

 the alburnous tubes are arranged in ridges beneath the cortical ves- 

 sels, and the number of these ridges at the base of each leaf corre- 

 sponds with the number of apertures which pass from the leaf-stalk. 

 The position and direction of these tubes have induced naturalists to 

 consider them as passages through which the sap ascends ; but Mr. 

 Knight intends to show that they are reservoirs of fluid secreted by 

 the bark, which they retain till it is absorbed by the surrounding 

 cellular substance. Having ascertained, by injections, that the al- 

 burnous tubes which descend from the base of an annual shoot are 

 confined to one side of the stem, and to the external annual layer of 

 wood, Mr. Knight made deep incisions at the bases of many annual 

 shoots of young trees, in such a manner as certainly to intercept all 

 communication with the stem by means of the alburnous tubes ; but 

 the shoots lived, and in the succeeding spring grew with considerable 

 vigour. In some small twigs, two incisions were made on opposite 

 sides, one a few lines higher than the other, so that all the alburnous 

 tubes might, in some part of their course, be interrupted ; yet the 

 sap continued to pass into the branches, and their buds unfolded in 

 the succeeding spring. 



All naturalists agree in stating that trees perspire most during 

 summer, when the leaves have attained their full growth ; but as 

 the alburnous tubes at that time appear dry and filled with air, it is 

 evident that the tubes do not convey the sap, but are intended to 

 execute a different office. 



But if the sap does not rise through the alburnous tubes, says 



