ANATOMY OF ACOTYLEDONS. 



141 



f 



748. Male Fern. 



Transverse section of the 



rhizome. 



749. Male Fern. 



Rhizome showing the scars (c) 



of the old fronds. 



structure and scars characterize the stems of the herbaceous ferns of Europe (figs. 

 748, 749). The fibro-vascular bundles of ferns, whether exotic or indigenous, con- 

 sist of a pale portion (fig. 747, v), formed of annular and 

 radiating prismatic (scalariform) vessels, surrounded by a very 

 narrow black zone (f), formed of woody 

 fibres. Trachese are invariably wanting. 



A few other acotyledonous families con- 

 tain fibro-vascular bundles in their stem ; 

 in Mosses and Hepaticce the stein is com- 

 posed of elongated cells, which sometimes 

 become fibres ; the tissues of Lichens, Fungi, 

 Algae, &c., are entirely cellular. 



Root. The roots of the higher acoty- 

 ledons, such as ferns, present the same 

 structure as the stems ; i.e. bundles of fibres 

 and vessels, surrounded by cellular tissue; 

 these roots are always adventitious and often 

 aerial. In the lower acotyledons they are formed of cells which reach the ground, 

 and then lengthen and bury themselves. 



Leaves. The leaves of acotyledons present the same structure as their stems ; 

 in ferns, we find radiating prismatic vessels and black fibres ; in Marsileacece, the 

 nerves are numerous ; in Lycopodiacece, the leaf is a cellular plate traversed by a 

 single fibro-vascular bundle ; in Mosses and Hepaticce, the nerves are represented by 

 elongated cells ; in the lower acotyledons, the leaves and stem are represented by a 

 frond entirely composed of cellular tissue. 



Reproductive Organs. Antheridia are little sacs, at first perfectly closed, then 

 opening at a certain period at one point of their surface, and emitting by this 

 opening a mass of corpuscules, usually cohering by means of a mucilaginous liquid ; 

 these organs are considered analogous to anthers ; we shall explain their nature in 

 the description of the Orders. 



Spores are little membranous sacs, full of liquid, which germinate by lengthening 

 at some undetermined point of their circumference, and develop into a little plant 

 similar to that which produced them. Spores are formed in particular cavities, 

 called sporangia ; they are the analogues of seeds, with regard to their functions, but 

 they possess neither coats, caulicle, radicle, plumule, nor cotyledons ; they are 

 developed freely in the sporangium, and never adhere to its walls, as the seeds of 

 cotyledons adhere to their placenta. The sporangium, which fulfils the functions of 

 a carpel, has neither style, stigma, nor ovarian cavity ; it is filled with a con- 

 tinuous cellular mass, in the midst of which are certain isolated cells, destined to 

 reproduce the plant. We shall explain the spores and sporangia when describing 

 the characters of the Orders. 



