46 REPORT ON BOTANY, MDCCCXLI : 
Schleiden, is the title of a treatise which was read to the 
Academy of Sciences at St. Petersburg!!, in 1839, hut which 
was only published at a subsequent period. The author first 
speaks of the parenchyma of the pith and bark, and says : — 
The cells are almost all globular or elliptical ; the connection 
between the separate cells is so loose, that they are generally 
torn asunder by one incision, so as to render it a rare occur- 
rence to see a cell which has been cut through. The sap, 
which in its youngest state always occupies the intercellular 
spaces, retires during its gradual drying up into the commissures 
(Fugen), and there forms a slight distention, filling up the 
vicinity of two cells. On the cells being separated, as described, 
the point of contact exhibits itself as a circle or ellipsis, sur- 
rounded by a slight elevated ring. Meyen has delineated these 
round circles from the Oncidum juncifolium, in which plant 
such a loose cellular tissue likewise occurs, and considers them, 
wrongly, as it appears to the author, large pores. The 
author has convinced himself, by researches and comparison 
in an infinite number of cases, that all porous canals proceed 
from the primary cell-wall ; and if they do not seem to reach 
as far as that, they are then only fragments of a canal which 
has been cut through. Such perfect canals are, however, 
never seen to terminate in an intercellular space, nor even 
upon a part of the cell-wall, which confirms Mohl’s view. The 
contents of the cells of parenchyma, always consist, in the 
first instance, of mucus in little globules, or of starch, both 
almost always covered with chlorophyll. It is of frequent 
occurrence amongst the Cactacece^ that the starch is the 
bearer of the chlorophyll; and, in this instance, it may 
readily be observed, that the starch, after having been libe- 
rated from the chlorophyll through means of alcohol, is always 
a long time before it acts upon iodine, as for instance, in 
Opuntia hrasiliensis. Besides the ordinary cells of paren- 
chyma, we also find, in very many Cactacece, cells of two or 
three times the size of the former, distributed in the bark as 
well as in the pith, which are entirely filled with vegetable 
mucus. This mucus has also a kind of organization. It forms 
a globule, and is very finely marked on the surface with small 
438 
