PHYSIOLOGICAL BOTANY. 267 



seeds germinating upon mercury, do not appear to me of 

 any importance. 



A remark which has already been frequently made, is 

 repeated by H. Jaubert, in the Compt. rend., 1845, ii, 

 360, namely, that on that side of a tree on which the 

 branches are strongest, strong roots also exist. He says 

 that he has very frequently found this to be the case in 

 digging up trees in Sologne. It may be well to recall 

 to mind, since these observations correspond with the 

 view, that the nutritive fluids ascend through the spiral 

 and dotted vessels, and as these vessels do not anastomose, 

 they ascend from the root in a straight direction. That 

 the branches, however, assume curves, like the roots, an 

 instance of which is here afforded, appears to be acci- 

 dental. 



TREVIRANUS has described a remarkable Formation of 

 Tubers, in Sedum amplexicaule. D. C. Bot. Zeit., 1845, 

 p. 265. In this plant, says he, the new shoots which 

 are destined for reproduction are much thickened for 

 about the length of an inch at the summit ; the leaves at 

 this part are also closely crowded, whilst at the lower 

 part of the shoot they are scattered. About the period 

 of the summer solstice, not only the main stem, which 

 has flowered, dies, but also the lateral shoots, the thick- 

 ened points of which constitute the above newly-formed 

 living shoots. On examining the latter, we find, com- 

 pletely incased by the dried sheath-like basis of the 

 leaves, a cylindrical mass of cellular tissue, the cells of 

 which contain granules of starch, and the centre of which 

 is occupied by a small ring of fibres and vessels ; at its 

 point is a bud consisting of the rudiments of a few leaves, 

 and which is marked with the scars of fallen leaves. It 

 is a tuber, formed by the confluence of closely- crowded 

 leaves. About the middle of August these tubers emit 

 new leaves ; these clothe the next year's stem, which ter- 

 minates in a flower; they are not, however, sheathing 

 like those which surround the tubers, but semi-cylindrical, 

 like the leaves of Sednm acre, reflexwn, &c. 



