Page:Proceedings of the Royal Society of London Vol 1.djvu/332

Rh Mr. Knight, it must pass the cellular substance ; and to show that the cellular substance is pervious to ﬂuids, he quotes an instance from a preceding communication, in which bark was generated on the surface of the cellular substance of pollard oaks. A new expe— riment is also related in conﬁrmation of this opinion. Various branches of two years old were cut from different trees; and after the cut surface had been covered with a cement impermeable to water, a portion of the bark was detached from each, so as to expose the Sur— face of the albumum. They were then immersed in coloured infu- sions for twenty hours, and were found to have imbibed the colour between the albumous tubes, apparently through the cellular sub- stance.

When an incision is made into the albumum near the root, and sap is seen to ﬂow from it, it may be observed to run even more abundantly from the upper surface of the incision; and since the quantity which exudes is full a hundred times more than was pre- viously contained in the albumous tubes, it appears evident that it is raised through some other channel.

Mr. Knight concludes, therefore, that the sap ascends through the cellular substance, and conceives that part to be so organized as to permit the sap to escape more readily upwards than in any other di- rection ; and, by its alternate contraction and expansion, to be fully capable of propelling the sap with all the impulse which it is known to have in the spring.

The albumous tubes appear to the author to answer also another purpose, since their cylindrical form occasions the strength of the materials employed to be the greatest possible.

The author concludes by observing, that though he retracts an opinion formerly entertained respecting the ascent of sap through the albumous tubes, yet his opinions concerning its subsequent motion through the central vessels, leaves, and bark, remain unchanged.

Mr. Goldingham’s observations are prefaced by a short account of the instruments employed, and some general remarks upon the cir- cumstances necessary to be attended to, in drawing inferences from them. Two telescopes were employed, both made by Dollond, of 3% feet focal length, with a magnifying power between 70 and SO; and the time observed by a good clock, with gridiron pendulum, was deduced froin the transit of the sun nearest to the eclipse, and veri— ﬁed by the next preceding or following transit.

The longitude of the place of observation is given, as determined from numerous observations of various kinds, that it may be com- pared with that deduced from each eclipse by means of the lime given in the ephemeris.

In noting each observation, the state of the weather is attended to,