422 KANSAS ACADEMY OF SCIENCE. 



containing water of a greater gravity. A difference of less than one- 

 millionth of the weight of water between two cells is sufficient to 

 cause osmose from cell to cell. This feature, together with the prin- 

 ciple of capillarity, as shown in the size of the cell, explains why there 

 is a limit to the height of any tree. 



The heaviest water, or sap as we call it, is always in the leaves and 

 bark : because evaporation is there constantly going on and the 

 gravity of the sap thus increased. The sap is prepared in the leaves 

 and bark. 



The spongioles, the roots, the pith, the wood, the leaves, the bark, 

 and the fruit of every tree and plant constitute the several depart- 

 ments of a chemical laboratory, in which the sap received is elabo- 

 rated and converted into the productions peculiar to that plant or 

 that portion of the tree or plant. Carbonic-acid gas is absorbed from 

 the air and combined with the mineralized water taken from the 

 Barth to form the various carbohydrates from which all the products 

 of the tree or plant are formed. In case of the tree cacti, as Opuntia 

 arborescens, Cereus giganteus, etc., much of the water needed is not 

 from the earth, but is absorbed from the air through especially-con- 

 structed cells. The sectored clusters of wood cells or vascular tissue 

 are arranged at, regular intervals within and completely surrounded, 

 bark and all, by the soft, cellular, parenchymatous tissue of the stem, 

 which is abundantly su^jplied with chlorophyl, and performs the 

 functions of both leaves and roots. The roots themselves, while they 

 do absorb some moisture and minerals from the earth, are mainly for 

 the purpose of keeping the plants in an erect position. 



The spongioles and root-hairs are always hungry and absorb more 

 than the cells can hold. The surplus is pushed back into the ceils 

 above, thus aiding the osmotic pressure. They have a selective ca- 

 pacity, and take from the soil, not everything in it, nor everything in 

 the water in the soil, but only those mineral ingredients which are 

 needed for use in the tree or plant. This they do by a faculty analo- 

 gous to what we call taste in animals. For example, asparagus, the 

 Russian thistle, the atriplexes, some of the goosefoots, and some of 

 the grasses, such as Distichlis spicata, Spartina gracilis, and finetop 

 salt-grass, thrive in a saline soil, where most other plants could not 

 live. Any plant will live in any soil where the food that it likes is 

 abundant and the food that it dislikes is not too plentiful. 



It often happens that two very dissimilar plants grow in the same 

 soil in close proximity without interfering with each other; in fact, 

 they are mutually helpful, for the reason that each one takes from the 

 soil materials that the other does not like and does not want. Beech 

 and maple trees are a case in point. Totally different in their natures, 

 they live harmoniously together and are mutually helpful. It might 



