6 BOTANY. 



Laticiferous Tissue, or Cinench7/ma, 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 late.v, Avhich, at first transparent, subsequently 

 becomes variously colored. Physiologists 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, 

 cj/sts, resercoirs 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. 



II. COMPOUND ORGANS OF PLANTS. 



I. Okgans of Nutrition or 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, Avax, silica, carbonate 

 of lime, (Sec. 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 cl )se according to the 

 greater or less amount of moisture in the atmosphere. The stomata com- 

 inunicatc with intercellular spaces, lined by the above-mentioned prolonga- 

 tions of the cuticle, called cistomata. 

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