274 Mr. A. Henfrey on the Progress of Physiological Botany : 
also in the extensive district of North America, where no more 
than a few insignificant species are known to exist. It is in the 
richly fertile and woody district of Columbia that the genus 
Bulimus is represented with a magnificence little inferior to that 
of the Philippine Islands : here they are large enough and suffi- 
ciently abundant to be roasted and eaten by the aborigines, as a 
frequent article of food. Several fine species, entirely new to 
science, have been collected in Venezuela and New Granada by 
Mr. Linden, an assiduous botanical traveller, only within the 
last twelvemonth, at an altitude of 5000 to 8000 feet, and 
many more, no doubt, dwell in undisturbed solitude in the vast 
interior of that immense continent. It is extremely probable 
that a large portion of South America yet remains to be explored 
by the adventurous naturalist, inclosing a fine expanse of forest 
country, grand in extent, rich in foliage, and possessing all the 
elements favourable to the growth and beauty of arboreal mol- 
lusks. 
XXVIII. — Reports on the Progress of Physiological Botany. 
No. 3. By Arthur Henfrey, F.L.S. &c. 
On the Growth of Leaves. 
In that remarkable book, Hales’s ^Vegetable Staticks,’ we find 
the account of an experiment made to determine the mode of 
growth and expansion of leaves. The method Hales adopted was 
to tattoo^ as it may be called, young leaves with punctures made 
by means of a little instrument on which pins were fixed at de- 
terminate distances in parallel rows. In the fig-leaves on which 
he experimented he found that the punctures were separated from 
one another during the growth, but maintained their relative di- 
stances unaltered, and from this he concluded that the growth 
and expansion were owing to the dilatation of the vesicles in 
every part.” In his figures, however, it may be noticed that 
the leaf has grown more at the borders and apex than within the 
punctures. 
Similar experiments have recently been made by M. Gaudi- 
chaud*, and he makes the following meagre statements in regard 
to the petioles and leaves. (The marks were made on young- 
plants of the horse-chestnut raised from seed.) The marks made 
on the petioles increased their distance two or three times the 
diameters, equal or unequal, of the original measures, and the pro- 
portions of the upper parts generally exceeded those of the lower. 
It might be imagined that the blades of the leaves would be 
* Comptes Rendus, May 10th, 1817. 
