10 
INFLUENCE OF SOLAR LIGHT ON VEGETATION. 
saccharine matter is formed in the alburnum of trees in the spring, which contained 
none in the winter : but M. Dutrochet was not acquainted with these circumstances, 
nor with others published in the Philosophical Transactions, by which I conceive 
myself to have proved that it is through the cellular substance of the alburnum^ and 
not through its tubes, as I once though t, that the sap ascends." 
M. Dutrochet corresponded with Mr. Knight on this his new view, but as slow 
progress only could be made by letters when the distance between the parties was 
nearly five hundred miles, he resolved to pay Mr. Knight a visit, an act which 
that gentleman considered as very honourable to his zeal, particularly as he did not 
speak, though he read, English. " He spent nearly three weeks with me, and our 
opinions before we parted became perfectly in unison. We both agree that the water 
and nutriment absorbed from the soil ascend through the cellular substance of the 
alburnum, and pass through vessels, cellular in structure, which surround the 
bundles of spiral tubes. That the nutriment absorbed becomes the true sap, or 
living blood of the plant, by exposure to light in the leaf ; that it descends by the 
hark (wherever plants have bark), by which the matter that forms the layer of 
alburnum is deposited, and that, whatever portion of the true sap is not thus 
expended, sinlcs into the alburnum through the misnamed medullary processes, and 
joins the ascending current. As autumn, however, approaches, the expenditure of 
sap diminishes; and it then accumulates in the alburnum, to be employed in 
forming the young shoots and leaves of the ensuing spring. I am in possession of 
a thousand facts to support this hypothesis, but not of one in opposition to it. Sir 
E. Smith had mistaken my meaning respecting the central vessels, though I must 
admit that I did not express myself with sufiicient clearness. I am quite certain 
that neither the spiral tubes, nor the threads which compose them, carry any 
aqueous fluid." 
With these high testimonials before us, we conceive that we have commenced 
a series of articles of great consequence, under favourable auspices, and hope, ere 
long, to add a few remarks in elucidation of terms which at present may be rather 
abstruse to the young student. 
INFLUENCE OF SOLAR LIGHT ON VEGETATION. 
The interesting papers in the late numbers of your Magazine of Botany on the 
" Influence of Light on Vegetation," induce me to ofler a few remarks which may 
assist in any researches into the subject. 
The eflects of light on the vegetable world, whether upon the fruit, leaves, or 
blossoms of its members, present, indeed, a beautiful subject. A blossom seems 
to feed on light, expanding in the morning to imbibe it, and closing at night, as 
if to sleep, sated with light. Many even closed during the eclipse of May ISthj 
1836, near Belfast, where the obscuration was considerable ; proving thereby, that 
