6 BOTANY. 
LaticireRous Tissur, or Cinenchyma, consists of long homogeneous tubes, 
branching and anastomosing like the blood-vessels of animals. Their walls 
exhibit no markings, but vary in thickness. They contain and conduct a 
granular liquid matter called datex, which, at first transparent, subsequently 
becomes variously colored. Physjplogists differ as to the origin of these 
vessels, some supposing them to be formed by linearly arranged cells, whose 
walls are absorbed at the eXtremities, so as to form a continuous tube in which 
the latex subsequently flows ; while others, again, maintain that the current is 
first established in the intercellular spaces, and that the inclosing wall is 
formed afterwards. 
There are no elementary forms of tissue other than those already mentioned, 
the rest being simple modifications of the above. The various air vessels, 
cysts, reservoirs of secreted matter, &c., are either intercellular spaces, or 
cells filled with air or with peculiar secretions. The air cells are seen in pecu- 
liar modifications in the stems of many water plants and grasses. | 
Il. COMPOUND ORGANS OF PLANTS. 
I. Oraans or Nutrition orn VEGETATION. 
1. The General Integument. 
By the term General Integument, is meant the external cellular covering 
of the plant, composed, in most cases, of two layers, the cuticle and 
epidermis. 
The Superficial Pellicle, or Cuticle, is a very thin continuous membrane 
spread over the epidermis, and investing all parts except the stomata, down 
whose cavity, however, it sometimes dips, forming a very delicate lining. 
Some physiologists, with Mohl at their head, do not admit this as a separate 
membrane from the epidermis, supposing it to consist of the external coat of 
the cell thus separated from the protoplasm ; others, again, suppose it to be a 
secretion from the cell, which, forming first on the inside, transudes to the 
outer surface. The epidermis, which lies subjacent to the cuticle, is found on 
all parts of the plant exposed to air excepting the stigma. In parts habitually 
submerged it is replaced by a simple cuticle. The epidermis is composed of 
cells, generally tabular, and arranged in a greater or less number of layers, 
these cells being bounded by flexuous or straight lines, containing either a 
colorless liquid or other substances, as resinous matter, wax, silica, carbonate 
of lime, &c. The stomata are openings between some of the cells of the 
epidermis, by which a communication is established between the air and the 
subjacent parts. They generally consist of two semilunar cells, surrounding 
an oval slit, as lips inclose the mouth. They open and close according to the 
greater or less amount of moisture in the atmosphere. The stomata com- 
municate with intercellular spaces, lined by the above-mentioned prolonga- 
tions of the cuticle, called ctstomata. 
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