STEMS, LEAVES, AND BUDS. 
49 
are seen at an early period. Finally, the mother cells are per- 
fectly absorbed, the inner cells becoming wood cells, the ex- 
ternal, cambium, &c. Another process yet takes place during 
the production of lateral anastomozing branches ; a cloudy, 
slimy, gummy liquid is produced in a certain series of cells of 
the parenchyma, from which a layer is precipitated, by which 
the parenchymatous cell is converted into a spiral or reti- 
culated fibrous cell. 
I have endeavoured to represent the theory of the author 
in the context, and have mentioned, that I consider the doc- 
trine of the cytoblast as the producer of the young cells in a 
mother cell, the latter of which is finally absorbed, as a mere 
hypothesis, founded upon imperfect observation. I do not 
know of any profound observer who has adopted it. Foreigners, 
when talking of cytoblasts, merely mean the nucleus in many 
cells, the existence of which no one denies ; they never allude 
to the mother cell. An example of it has been given above. 
Schwann has adopted Schleiden’s views, and applied them to 
the animal world. I think, perhaps the animal cell, in this 
respect, may be formed in a way exactly opposite to the 
vegetable cell. 
It has always been a question, whether the spiral vessels 
are air tubes, or whether they carry the juices for nutrition ? 
I myself have twice changed my opinion regarding it, because 
it was more my object to arrive at the truth than to insist 
upon being right. Dr. Schleiden despatches this question 
very quickly. He says, “ I found, almost without exception, 
in all Cactacem, that the vessels, as they issued from the 
cambium, were filled with air. Indeed, I must confess, that 
I cannot conceive how any one, who has examined a great 
number of plants with attention, and only applies sound logic, 
can set up the doctrine, that the spiral vessels, and the woody 
fibres associated with them, are intended to carry fluid. 
Never and nowhere is a fluid found in them, excepting during 
a short time in the spring, in the forest trees of our' own 
climate, which may be accounted for very simply, by the su- 
perabundance of the rising sap, and the permeability of the 
cell-membrane, and which, being only a periodical phenomenon, 
441 
