rer 
278 FOUNDATIONS OF BOTANY 
on the carbon dioxide gas which the plant absorbs, that is, 
arranged about rather large air chambers. 
Reproduction is of two kinds, sexual and asexual, and 
the organs by which it is carried on are complicated and 
highly organized. An alternation of generations occurs, 
that is, the life history of any species embraces two forms: 
a sexual generation, which produces two kinds of cells that 
by their union give 
Sane is rise to a new plant; 
the asexual genera- 
tion, which multiplies 
freely by means of 
f special cells known 
Law 4 
oe eat 
KR a a8 spores. 
ay : Le THE STUDY OF 
Fig. 202. —Part of Female Thallus of MARCHANTIA 
M. disjuncta. (Enlarged.) 395 -Gecureemal 
Marchantia grows on soil 
or rocks in damp shaded places and is widely distributed. 
336. The Thallus. —In general form the thallus bears some resem- 
blance to that of some of the lichens, as Parmelia, but is plainly 
different in color, mode of branching, and internal structure under 
the microscope. Under the microscope (see below) the individual 
cells may be compared with those of the medullary layer in Physcia. 
Note the color and general shape of the thallus and study care- 
fully the mode of branching. The origin of the growing cells is at 
the tip, but cells so originating afterward multiply more rapidly, so 
that the tip comes to be in a notch. 
Viewing the thallus as an opaque object, note the diamond-shaped 
network on the upper surface and the dot-like circle in the middle 
of each diamond. 
Examine the under surface for (1) rhizoids and (2) scales. 
Sr, female receptacle ; c, cups with gemme. 
