48 ANATOMY AND PHYSIOLOGY OF 



terized by cliemists, and no re-agents for tliem have been made 

 out, vegetable anatomists are not in a position to make out their 

 distribution in the Vegetable Kingdom, or their importance to 

 the plant. 



Sugar is very widely distributed, especially cane-sugar, since it 

 not only replaces starch in many plants at the time just preced- 

 ing flowering, as in the Sugar-cane, the Beet, &c., but still more 

 frequently precedes the deposition of starch in an organ, and is 

 also formed at the solution of the starch as in trees in Spring, in 

 germinating seeds, &a Neither Cane nor any other sugars (grape- 

 sugar, fruit-sugar, mannite, &c.) are objects for microscopic obser- 

 vation, since they are dissolved in the cell-sap, and we are without 

 re-agents for them. 



Although occurring in a fluid form, the fixed oils are readily 

 detected by their refusal to mix with water, and by their strong 

 refracting power, when they occur in abundance, as they 

 do principally in the seeds of many plants, more rarely in the 

 coats of the fruit (in Olives, many Palms, &c.), still more rarely in 

 the organs of vegetation (tubers of Oyperus esculentus). But 

 when they exist only in smaller quantities, as is the case in a great 

 number of plants, they escape observation by the microscope, since 

 they are not then separated as clearly visible drops floating in the 

 cell-sap, but are combined with the proteine substances. The 

 essential oils, when produced in large quantity, usually com- 

 pletely fill isolated cells, or groups of cells and cavities which lie 

 between cells, and then are easily discovered : on the other hand, 

 m very xnany ca.es they seem t^ exist in such small quantities', 

 that they are wholly dissolved in the cell-sap ; at all events they 

 cannot be visibly demonstrated in the greater number of petals. 



All plants prepare a more or less abundant quantity of organic 

 acids (oxalic, malic, citric, tartaric acid, &e), wliich are found only 

 in exceptional cases in a free condition, usually combining with 

 bases into acid-salts dissolved in the cell-sap , and many of the 

 inorganic acids, which the plants receive from without, remain 

 undecomposed. The greater part of these salts, especially those of 

 the alkaline bases, escape microscopic examination by their solu- 

 tion in the cell-sap ; but there is scarcely one of the higher plants 

 in which some organ or other does not secrete in the cavities of its 

 cells insoluble salts of the earths with organic or inorganic acids, 

 in the form of crystals. This usually takes place in cells which 

 contain no granular organic structures; but crystals, and chloro- 

 phyll granules, and the like, do not necessarily exclude one 

 another. In particular cells situated at the upper sides of the 

 leaves of many tJrticaceae, a g.^ in Morus^ Fious elastica, &c., is 

 found what appears to be a peculiar organic structure (a coni- 

 cal projecting process of the internal wall of the cell^ formed 

 of cellulose), upon wliich crystals are agglomerated as upon a 

 nucleus. 



