
564 SHAVINGS EXAMINED MICROSCOPICALLY. 
upon each other until they have lost their almost spherical 
outline, and flat sides have made their appearance. We may 
ilustrate the form of vegetable cells by blowing soap-bub- 
bles with a tube. As long as we blow but one bubble at a 
time, they remain spherical in form and represent the simple 
Protophyia, but if we blow one after another until a string 
of them remain pendant from the tube we have a represent- 
ative of the slightly more complex plants growing submerged 
in water and known as alge. By placing the tube beneath 
the surface of the soapy liquid contained in a bowl and 
blowing we form a number of bubbles, which, on account 
of their being confined within the bowl, press upon each 
other almost equally and become many sided. The form that 
thus results is found on examination to be of a more or less 
perfectly geometrical outline, and such a mass very strik- 
ingly represents the cellular tissue we are examining, but to 
make it look still more like our section, we press a glass 
plate down upon the mass of bubbles, and thus we have the 
cavities cut across. But one other fact will be noticed 
through the glass plate, and that is that the bubble sections 
are for the most part six-sided, and such is also the case 
with the plant cells. This is the result of cutting through 
the regular geometrical form always caused by the mutual 
equal pressure of many spheres. In honeycomb we have 
another illustration of this fact; there the pressure has ap- 
parently been unequal, and the cell has become elongated 
into a six-sided prism. A precisely similar mode of aggre- 
gation is to be observed in vegetable tissues, and may be 
made evident by eutting two sections at right angles to each 
other. Such slices are known to microscopists as longitu- 
dinal and transverse sections; the first, in the case of wood, 
being taken lengthwise of the stem or branch, and the other 
across it. Asthe pressure is generally very unequal, perfect 
.. forms of the cells are the exception, and therefore the variety 
. Of outline of cells in vegetable tissues is very varied, 
. Which is hexagonal being the most common. As a plant 


