148 
Journal of Mycology 
[Vol. 10 
dally differentiated for the particular work. The “division of 
labor/’ is as marked as in animals of complex structure. It is, 
in fact, as pronounced and as advantageous as that witnessed in 
the highest stages of human civilization. 
Tissue. — The differentiation of cells and tissues referred to 
in the previous paragraph, is illustrated in our common plants — 
the herbs, shrubs, and trees. There is, for example, an epidermal 
system of tissues ■— the epidermis itself consisting of a compact 
layer of cells with their outermost walls much thickened, usually 
also cuticularized, affording to the delicate tissue beneath efficient 
protection against the elements or other untoward exigencies; 
between two specially modified (so-called guard-cells) a pore, or 
stomate, is formed; the stomates, though extremely small, num¬ 
ber hundreds to the square inch of leaf-surface and through these 
ample entrance is afforded' for carbonic dioxide, as well as free 
passage to oxygen and watery vapor — without which the various 
processes in nutrition and growth could not take place. Epi¬ 
dermal cells may develop in the form of hairs or scales — also 
protecting devices. There is also a system of woody tissue — 
either isolated strands as in the herbaceous stems, or a coalesced 
mass with cells much thickened and strongly lignified as in the 
shrubs and trees. In all of these plants, many of them of great 
size, the mechanical tissues are abundantly developed — essential 
for support of the various parts and the maintenance of the plant- 
form. Equally various and complex are the tissues and cells 
specially concerned in nutritive and reproductive processes. 
Mycelium. — If we pass from the common Flowering plants 
and Ferns to the next lower group, namely, the Mosses and 
Liverworts, les differentiation in the tissue is seen. There is no 
specially modified epidermis; there are no woody strands in the 
scale-like leaves — none even in the stems of the Mosses; and 
most Liverworts have no stems. There is, in short, less hetero¬ 
geneity in the cells composing the plant. If we turn to still lower 
plants, the group of Thai’-lo-phytes, which includes the Lichens, 
Fungi, Algae, and Slime Moulds, less complexity in tissue will be 
found; instead of great heterogeneity, marked homogeneity pre¬ 
vails. In some of the highest representatives of this great group 
of plants, as the Lichens, the Toadstools, the large “sea-weeds” 
(marine algae), there is a comparatively large and more or less 
complex form of plant body. Even the interior structure is 
found to be somewhat intricate in these plants; but yet the cells 
forming the more or less compact tissue are quite similar through¬ 
out — they have not become noticeably differentiated, have not 
assumed varied forms, as is seen in the tissues of a Fern or a 
Rose. The lowest plants exhibit the greater simplicity — a sin¬ 
gle cell may constitute the entire plant though this in a few cases 
becomes much extended and variously branched. The many- 
celled Thallophytes may develop a tangled mass or thick felt of 
