342 PRACTICAL COURSE IN BOTANY 
the base of the branches for knots or enlargements, like 
those seen at kn, Fig. 483. These are buds from which the 
leafy moss stems will develop. Do they correspond to any- 
thing observed among the thallophytes? Notice the rootlike 
filaments that extend under ground; how do they differ from 
the ones above ground? Why are they colorless? How 
do you know that they are not true roots? [67 (a), 379.] 
Sketch one of each kind of filament sufficiently enlarged to 
show the cells composing it. 
A protonema that arises directly from the spore is said 
to be primary, while those which sometimes spring from 
rhizoids above ground, or from stems or leaves, are 
secondary. The fact that a protonema can bud from parts 
of the fruiting stems shows that the two do not belong to 
different generations, but are merely successive stages of 
a single generation, and both together compose the game- 
tophyte. 
397. The leafy stage. —In their fully developed state 
the true mosses show a marked advance in organization over 
the liverworts. There is a distinct 
differentiation of the growing axis into 
stem and leaves, though no true roots 
care formed. The leaves are arranged 
spirally, on upright stems, while in the 
liverworts the vegetative body is 
either a flat, spreading thallus, or the 
leaves are arranged horizontally on 
opposite sides of a prostrate, or more 
or less inclined, axis. Sometimes a 
second set occurs, on the upper side 
Fic. 484.—Scapania, a Of the axis, but in this case the leaves 
liverwortwithleafy thallus, ap- are usually much smaller and inclined 
proaching the form of mosses i: 
and lycopodiums.(FromCout- to the horizontal arrangement, as 
TER’s ‘‘Plant Structures.’’) shown in Fig. ASA. 
398. The reproductive organs.— The antheridia and 
archegonia are borne in groups at the end either of the main 
