ELEMENTS OF ORGANIC STRUCTURE. 223 
Cellular Planis.—In those classes of vegetation which 
depart structurally to the least degree from the seed, and 
which belong to what are called the “lower orders,”* we 
find plants which consist entirely of cells throughout 
all the stages of their life, and indeed many are known 
which are but a single cell. The phenomenon of red snow, 
frequently observed in Alpine and Arctic regions, is due to 
a microscopic one-celled plant which propagates with great 
rapidity, and gives its color to the 
y a surface of the snow. In the chem- 
2@° ist’s laboratory it is often observed 
e a that, in the clearest solutions of 
salts, like the sulphates of soda and 
Fig. 27. magnesia, a flocculent mould, some- 
times red, sometimes green, most often white, is formed, 
which, under the microscope, is seen to be a vegetation 
consisting of single cells.’ Brewer's yeast, fig. 27, is nothing 
more than 2 mass of one or few-celled plants. 
In the mushrooms and sea-weeds, as well as in the moulds 
that grow on damp walls, or upon bread, cheese, etc., and 
in the brand or blight which infests many of the farmer’s 
crops, we have examples of plants formed exclusively of 
cells. 
All the plants of higher orders we find likewise to con- 
sist chiefly of globular or angular cells. 
All the growing parts especially, as the 
tips of the roots, the leaves, flowers, and 
fruit, are, for the most part, aggregations 
of such minute vesicles. 
If we examine the pulp of fruits, as that 
of a ripe apple or tomato, we are able, by 
means of a low magnifier, to distinguish 
the cells of which it almost entirely con- 
sists. Fig. 28 represents a bit of the flesh of a ripe pippin, 
Fig. 28, 
* Viz.: the Cryptogams, including Moulds, and Mushrooms, (Fungi,) Mosses, 
Ferns, and Sea-Weeds, (Alg@). 
