258 THE GARDENER. [June 



parent plant, if scientifically treated for that purpose, of which more 

 will be written hereafter. 



Pseudo bulbs, or pseudo tubers, of Orchids, are of green colour above 

 ground, thickening at the base of the stem. In the Dendrobium 

 they assume the form of an ascending stem, and bear on it the 

 beautiful ilowers. The function is that of a reservoir to supply to 

 the next pseudo bulb and llower nourishment. The pseudo (stem- 

 like) bulb of Dendrobium possesses the faculty, on division into cut- 

 tings, of throwing out aerial roots and forming a new plant : possibly 

 the joints in the stem are allied to nodes, if not identical. 



The organisation of the roots of the plant is so beautifully adapted 

 to the functions they have to perform, that they go, as it were, in 

 search of and to select their food, often long distances, penetrating 

 through crevices in the soil. The root-cells are considered to be the 

 immediate absorbers, and are easily and often replaced ; but there is 

 no sufficient reason for considering that in dicotyledonous plants 

 they are formed annually, as has been sometimes stated. Water in 

 some form, either as vapour or as liquid containing in solution 

 carbon dioxide (carbonic acid), ammonia, and saline elements, is the 

 medium by which plants absorb their food. 



So great is the attractive force of the liquid in a plant set in motion 

 by the action of these root-cells, and of a certain amount of heat 

 which is necessary, and of the cell-walls of the root, stem, and leaves, 

 that the absorbed liquid passes from cell to cell, filling them up, pass- 

 ing into the stem, distending the cell-walls, and enlarging the same, 

 and thence to the leaves, where it is elaborated, and the liquid is 

 called sap. This process of the strange phenomenon of liquids 

 attracting each other through a vegetable tissue, as the cell-w T all or 

 membrane of cellulose, is known by the name of osmose (osmosis, or 

 impulse): the outward flow is called exosmosis, the inward flow is 

 called endosmosis. Its power varies : some organic substances have 

 little or no osmose, others produce it to a great extent, and others 

 have a negative osmose. This osmotic action has been called hydro- 

 static pressure, and in grape-sugar it is very great, as may be readily 

 seen in the warmth of spring, when Vines bleed, as it is called, if cut 

 before the leaf-growth has commenced to utilise the sap. Schleiden 

 says that endosmosis is assisted by absorption of cell contents, caused 

 by evaporation of the watery fluid through the leaves : in other words, 

 as all the cells are filled with fluid, evaporation empties them, and 

 therefore the greatest flow of sap is where, and when, the plant has 

 most evaporating organs. 



A good example of the power of endosmotic force may be seen 

 sometimes in a vinery, when a young rod is carried up from an old 



