338 



THE MICROSCOPE AND ITS REVELATIONS. 



FIG. 217 



Archegonia of Marchantia poly- 

 morpha, in successive stages or de- 

 velopment. 



true Fructification, which is to be looked-for rather in plants growing in 

 more exposed places. Each of the stalked peltate (shield-like) disks con- 

 tains a number of flask-shaped cavities opening upon its upper surface, 

 which are brought into view by a vertical section; and in each of these 

 cavities is lodged an anther idium, composed of a mass of ' sperm-cells,' with- 

 in which are developed ' antherozoids ' like those of Chara (Fig. 154 H), 

 and surmounted by a long neck that projects through the mouth of the 



flask-shaped cavity. The wheel-like recep- 

 tacles (Fig. 214), on the other hand, bear 

 on their under surface, at an early stage, 

 concealed between membranes that connect 

 the origins of the lobes with one another, a 

 set of archegonia, shaped like flasks with 

 elongated necks (Fig. 217); each of these- 

 has in its interior an 'oosphere' or ' germ- 

 cell/ to which a canal leads down from the 

 extremity of the neck, and which is fertilized 

 by the penetration of the antherozoids 

 through this canal until they reach it. In- 

 stead, however, of at once evolving itself into- 

 a new plant resembling its parent, the fer- 

 tilized oosphere or ( embryo-cell ' develops 

 itself into a mass of cells inclosed within a 

 capsule, which is termed a sporangium; 

 and thus the mature receptacle, in place of archegonia, bears capsules or 

 sporangia, each of them filled with an aggregation of cells that constitute 

 the immediate progeny of the original germ-cell. These cells, discharged 

 by the bursting of the sporangium, are of two kinds: namely, spores, or 

 gonidial-cells, inclosed in firm yellow envelopes; and elators^ which are 

 ovoidal cells, each containing a double spiral fibre coiled up in its interioiv 

 This fibre is so elastic, that, when the surrounding pressure is withdrawn 

 by the bursting of the sporangium, the spires extend themselves (Fig. 

 218), tearing apart the cell-membrane; and they do this so suddenly as 

 to jerk forth the spores which may be adherent to their coils, and thus to 

 assist in their dispersion. The spores, when subjected to moisture, with 

 a moderate amount of light and warmth, develop themselves into little 

 collections of cells, which gradually assume the form of flattened fronds;, 

 and thus the species is very extensively multiplied, every one of the aggre- 

 gate of spores which is the product of a single germ-cell being capable of 

 giving origin to an independent individual. 



335. Musci. There is not one of the tribe of mosses whose external 

 organs do not serve as beautiful objects when viewed with low powers of 

 the Microscope ; while their more concealed wonders are admirably fitted 

 for the detailed scrutiny of the practised observer. Mosses always possess 

 a distinct axis of growth, commonly more or less erect, on which the 

 minute- and delicately-formed leaves are arranged with great regularity. 

 The stem shows some indication of the separation of a cortical or bark- 

 like portion from the medullary or pith-like, by the intervention of a 

 circle of bundles of elongated cells, which seem to prefigure the woody 

 portion of the stem of higher plants, and from which prolongations pass 

 into the leaves so as to afford them a sort of midrib. The leaf usually 

 consists of either a single or a double layer of cells, having flattened sides 

 by which they adhere one to another : they rarely present any distinct 

 epidermic layer ; but such a layer, perforated by stomata of simple- 



