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 sufli- 

 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 soUtude 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 



* Comptss Rendus, May 10th, 1847. 



