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 frimary, 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 

 are 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 

 of the axis, but in this case the leaves 

 are usually much smaller and inclined 

 to the horizontal arrangement, as 

 shown in Fig. 484. 



398. The reproductive organs. — The antheridia and 

 archegonia are borne in groups at the end either of the main 



Fig. 484. — Scapania, a 

 liverwort with leafy thallus, ap- 

 proaching the form of mosses 

 and lycopodiums. (From Coul- 

 ter's "Plant Structures.") 



