TYPES OF CRYPTOGAMS; PTERIDOPHYTESe 289 
cover with a large cover-glass, and examine with the lowest power 
of the microscope. Note: 
(a) The abundant root-hairs, springing from the lower surface 
of the prothallium. 
(6) The variable thickness of the prothallium, near the edge, 
consisting of only one layer of cells. 
(c) (In some mature specimens) the young fern growing from 
the prothallium, as shown in Fig. 211, B. 
The student can hardly make out for himself, without much 
expenditure of time, the structure of the antheridia and the arche- 
gonia (Fig. 211, A), 
by the codperation 
of which fertilization 
takes place on much 
the same plan as that 
already described in 
the case of mosses. 
The fertilized egg- 
cell of the archego- 
nium gives rise to 
the young fern, the 
sporophyte which 
grows at first at the 
expense of the parent 
prothallium but soon 
develops roots of its 
own and leads an in- A, under surface of a young prothallium ; ar, arche- 
dependent existence. gonia; an, antheridia; r, rhizoids; B, an older pro- 
+43 thallium with a young fern-plant growing from it ; 
. u -_— 
353. Nutrition l, leaf of young fern. (Both x about 8.) 
Fia. 211.— Two Prothallia of a Fern (Aspidium). 
The mature fern 
makes its living, as flowering plants do, by absorption of nutritive 
matter from the soil and from the air, and its abundant chlorophyll 
makes it easy for the plant to decompose the supplies of carbon 
dioxide which it takes in through its stomata. 
