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in dry weather. If a transverse section is made of one of these teeth, it is 

 found to consist of two rows of cells, divided by a central line, often having 

 little holes or split into two forks ; but behind this outer layer of coloured 

 cells is an inner row of soft bladdery cells. It is to the action of these 

 internal cells the teeth owe their hygroscopic nature. When the cells are 

 filled with water they pull the teeth inwards. 



In describing mosses the best way is to begin with the seed or spore. 

 This is very minute, and almost always of a globular form, sometimes 

 covered with little warts, sometimes smooth. In germination, the outer 

 coat having given way the inner sac protrudes, and bye and bye presents a 

 jointed thread, from which branches go off in various directions, and in time 

 it becomes a complete bunch of threads. This is called the protonema. 



In all true mosses it has this form. In the Hepaticae it takes a thalloid 

 form. From this the young moss begins to grow, and from one of these 

 sometimes will be found 20, or 50, or 100 young plants, all springing from 

 the protonema, or prothallium. Occasionally there is no fruit. In that 

 case the protonema is capable of being developed from roots, leaves, and 

 buds ; a single living cell is capable of producing a new colony of plants. 



In Funaria the old leaves fall off, and their basal cells will throw out 

 threads of protonema. 



As to the arrangement of the leaves, a very few have leaves in two rows. 

 One the Schistostega, and the other the great genus Fissidens. 



The Fissidens were very peculiar from the formation of the leaves ; which 

 are, as it were, double, and clasp the stem. Some extraordinary ideas had 

 been published as to how this was produced. Carl Miiller thought that the 

 small double part was the true leaf and the rest an outgrowth of the 

 nerve, which grew on and threw out an extension at the point and on the 

 back, and he called these the apical and dorsal laminae, the double portion 

 being the true lamina of the leaf. Another thought that the leaf split in 

 order to admit the stem. But if the leaf were so split this portion would 

 naturally be thinner than the other, and not contain the same number of 

 cell-layers, but in this case each half had the same thickness as the rest. 

 His friend Lindberg had put it in its true light ; he considers that the leaf 

 has its natural form, but placed edgewise, a row on each side of the stem, 

 and to each leaf is united a stipule, thus forming the double part, so that 

 in reality there are four rows of leaves, two of large size and two of small 

 size on the back, and these became adherent. That appeared the simplest 

 view of the matter. 



The leaf consists entirely of cells, which vary in form. There are two 

 principal forms, one prosenchymatons, ending in points, very commonly 

 hexagonal cells ; the other parenchymatous, having a square end, quadrate 

 or rectangular cells, and in that way is built up the tissue of the leaf. 

 Sometimes the lower part of the leaf has one kind of cell and higher up the 

 other. Sometimes it is so much thickened that the cells look like so many 

 dots, which is due to a thickening process in the cell. The surface of these 

 cells, and therefore of the whole leaf, might be quite smooth, or it might 

 project into several forms of papilla?. 



