CELU'LAR TISSUE. 19 



spect tlic importance this comparison will assif^n it. It con- 

 stitutes the basis, physically considered, ol' the vegetable 

 kinirdom. 



lo. The cells of common cellular tissue arc without visible 

 pores, yet the walls are permeable to Huids, as is proved by their 

 -sometimes lull, and at others emj»ty. This may also be 

 Mn.»> li by takiiij: a piece of the pith of the elder and letting a 

 part of it communicate with water and the whole mass will 

 become saturated with it ; and it is a fact well understood at 

 the present day, that animal and vegetable membrane, even 

 when not under the influence of vital power, is permeable to 

 fluids under certain circumstances ; that is when opposite sides 

 of the membrane are exposed to fluids of diflerent density. 

 Although all cells have been considered perfectly closed, and 

 in the great mass of cases this is no doubt true. Professor 

 Roeper has recently made some important observations on 

 the cells of the Sphagnum, and has demonstrated most satis- 

 factorally, the existence of apertures in these cells, and that 

 too, of quite large dimensions. He tirst proved tlieir presence 

 by the passage of the amylaceous grains of the vymphaca- 

 lutea into celis which had been previously examined, and found 

 free from any thing of the kind, but bv immersion in water 

 containing these grains, tliey were found to have entered the 

 cells. During his examination of the elongated cells of the 

 Sphagnum obtiisijolium, he unexpectedly observed in some of 

 the cells animalcules, and some of them making aj)parent 

 efforts to escape ; and after watching the attempts of one for 

 ppveral hours, he was gratified by seeing it issue from the 

 cell ; but instead of issuing into the water in which the cells, 

 for examination, were placed, he entered another cell lying 

 contiguous to the opening through which he passed, and Roe- 

 per remarks that the posterior part of its body was engaged 

 in the first cell, while tlie anterior part had possession of its 

 new dwelling, dc sa nouvcUe dcmcurc ! 



IG. The cellular tissue possesses the hygrcmetrical property 

 in a high degree, and this power is applied in the economy 

 of vegetation to most important purposes. The anthers burst 

 by the exercise of this property ; most of them in dry weather 

 by the contraction of the cells on one side while those on the 

 other remain distended. The bursting of capsules is the ef- 

 fect of the same cause, and one may convince himself of the 

 truth of this assertion by closely inspecting the bursting of 

 the common "Touch-me-not," the inner cells have become in 

 maturity compressed lirmer and smaller, while the outer ones 

 are in moist weather turged and elastic, and by slight agita- 



