400 
PHYSIOLOGY. 
BOOK II. 
If, however, the fine capillary ramifications of the 
cinenchyma upon the surface of plants will satisfy the en- 
quirer, the movement of cyclosis may be readily found 
in almost any lymphatic hair, provided the microscope em- 
ployed will magnify 350 diameters. Tradescantia virginica 
is usually employed for this purpose, but in reality any 
hair will show it, especially if the latex be milky. It is then 
seen, to use the words of my lamented pupil, Mr. Slack, that 
each joint of the hair consists of an outer glassy colourless 
case, enclosing the colouring matter. A nucleus (cytoblast) 
is situated at the base of the joint, and currents of small 
particles appear to pass near it or over its surface. Those 
currents may often be traced through their whole course 
around the cell, ascending in one part, descending in another, 
and sometimes two uniting into one. The structure of each 
joint of the hair appears to be an outer glassy tube, with lon- 
gitudinal striae ; between this and the colouring matter the 
moving fluid with its particles exists. The coloured fluid of the 
hair seems to be enclosed in a membranous sac, which forms an 
axis round which the moving fluid revolves. The cytoblast 
must also be external to the sac, as it is in connection with 
the currents. [Trans. Soc. Arts, xlix. p. 41.) 
The course which is taken hy the sap, after entering a plant, is 
the next subject of consideration. The opinion of the old 
botanists was, that it ascended from the roots, between the 
bark and the wood: but this has been long disproved by 
modern investigators, and especially by the experiments of 
Knight. If a trunk is cut through in the spring, at the 
time the sap is rising, this fluid will be found to exude more 
or less from all parts of the surface of the section, except the 
hardest heart-wood, but most copiously from the alburnum. 
If a branch is cut half through at the same season, it will be 
found that, while the lower face of the wound bleeds copiously, 
scarcely any fluid exudes from the upper face ; from which, 
and other facts, it has been fully ascertained that the sap 
rises through the wood, and chiefly through the alburnum. 
It is related by Berthellot, that the people of the Canaries 
tear off the bark of the poisonous Euphorbia canariensis, and 
suck the limpid sap of the alburnum, which, during its ascent 
