Vl] SEPARATION OF CELLS 71 



or to facilitate the escape of such gases or water vapour 

 from the cells to the exterior ; though they are often 

 utilised by the way as reservoirs in which air may collect 

 for the time being and float the organs on water e.g. 

 Pistia, Pontederia, Trapa, &c. 



The separation of cells is often carried to complete 

 isolation, however, as in the formation of spores, pollen- 

 grains, and in other cases. The fine dust of minute spores 

 which escapes from a puff-ball, a moss-capsule, and the 

 yellow powdery pollen from the anthers of Lilies and 

 other flowers are all separated cells which have thus 

 been isolated from a continuous cell-tissue by the dis- 

 solution of the middle lamella, and in a vast number of 

 the lower plants Algae, Fungi, and Bacteria the whole 

 plant-structure thus breaks up into single cells, and 

 during a great part of the life of the organism the latter 

 consists of a single isolated cell only. We shall see, 

 moreover, that many contrivances in plants depend on 

 the partial or complete separation of the cells by the 

 splitting of the middle lamella. That this splitting of 

 the middle lamella is really due to its more or less ex- 

 tensive dissolution, is borne out by experiments wherein it 

 is artificially dissolved. When a potato, apple, turnip or 

 other soft organ is boiled, the cells are isolated owing to 

 the action of the hot water on the middle lamella, a 

 process very similar to what occurs naturally when fruits 

 like the Tomato, Peaches, and Grapes, &c. ripen to a pulpy 

 mass of isolated cells. Similar isolations occur in the 

 alimentary canal of every school-boy who eats, and suc- 

 cessfully digests, an unripe apple or pear ; or of a horse, 

 cow, sheep or other herbivorous animal which eats grass 

 or other leaves, grain, &c., and cells thus separated under 

 the action of the intestinal fluids occur in the excrement 

 of all herbivorous animals. In wood and other resistant 



