416 



THE MICROSCOPE. 



But in this case the linen should be pressed gently, and a portion only 

 of the water expelled, the remainder being poured into the bottle, and 

 the process repeated as often as necessary. 



Sporangia are collected more frequently by the last than the 

 preceding methods. When carried home, the bottles will apparently 

 contain only foul water ; but if it remain undisturbed for a few hours, 

 the Desmidacese will sink to the bottom, and most of the water may 

 then be poured off. If a little filtered rain-water be added occasion- 

 ally, to replace what has been drawn off, and the bottle be exposed to 

 the light of the sun, the Desmidacese will remain unaltered for a long 

 time." 



fig. 197. a, elementary cells. I, branched cellular tissue. 



The Desmidacese prefer an open country. They abound on moors 

 and in exposed places, but are rarely found in shady woods or in deep 

 ditches. To search for them in turbid waters is useless ; such situa- 

 tions are the haunts of animals, not the habitats of the Desmidaceae ; 

 and the waters in which the latter are present are always clear to the 

 very bottom. 



To proceed in our inquiry : we now find the cell converted into 

 other forms, and the transparent membranous cell-wall becoming 

 thickened ; spontaneous fissure then takes place ; and thus is formed 

 a series of connected cells variously modified and arranged, according 

 to the conditions under which they are developed and the functions 

 which they are destined to exercise. The typical form, as we have 

 before observed, of the vegetable cell is spheroidal ; but when deve- 

 loped under pressure within walls, or denser tissues, they take other 

 shapes, as the oblong, lobed, square, prismatical, cylindrical, fusiform, 

 muriform, stellate, jttamentous, &c. : it is then termed Parenchym ; 

 and the cells woven together are called cellular tissue. In pulpy 

 fruits the cells may be easily separated one from the other : a thin 

 transverse section of a strawberry is represented at No. 15, Plate 

 XVI.: within the cells are smaller cells, commonly known as pulp. 

 Fig. 197, a, is the elementary form of oval cells or vesicles, passing 

 on to form branched cellular tissue, b. Kemarkable specimens of the 



