16 VASCULAR CRYPTOGAMS 



is always a prothallium, which is usually a green plate of tissue lying flat 

 on the soil, very commonly lobed or reniform in shape, sometimes 

 microscopic, but often quite visible to the naked eye, from to \ an inch 

 in diameter, and constituting, with its organs of reproduction, the oophore, 

 oophyte, or sexual generation. The prothallium usually disappears as soon 

 as the non-sexual generation has firmly rooted itself in the soil ; but in 

 Gymnogramme (Filices) it attains a larger size, and continues its existence 

 for a considerable time, producing a succession of reproductive organs. 

 The oophyte never becomes differentiated into stem and leaves, as 

 in the Muscineae, nor does it contain any vascular tissue. It usually 

 consists of only a single layer of cells filled with chlorophyll, except a 

 marginal cushion, where there are several layers. Here it puts out into 

 the soil numerous colourless elongated cells, the organs of attachment, 

 or rhizoids, 1 among which, or scattered over the whole of the under 

 surface and margin, are the archegones and antherids. True vegetative 

 budding takes place but rarely on the prothallium ; but it sometimes, 

 in certain Filices, exhibits apogamy, the sporophore springing directly 

 from it, without the intervention of the sexual organs. In some Lyco- 

 podiacese and in the Ophioglossaceae the prothallium is subterranean, 

 destitute of chlorophyll, and cylindrical or tuberous. In the Hymeno- 

 phyllaceae (Filices) it is often filiform. In the isosporous families the 

 prothallium is most commonly monoecious, less often dioecious. In the 

 heterosporous families it is far less fully developed. That which arises 

 from a megaspore is very small, formed within the spore, and at no 

 period maintains an independent existence ; while that developed 

 within a microspore is still more rudimentary. 



The archegones of Vascular Cryptogams are produced on the pro- 

 thallium, usually on the under side of the cushion. Each archegone 

 consists of a swollen basal portion or venter, and a neck, usually composed 

 of four longitudinal rows of cells ; the venter is buried in the tissue 

 of the prothallium, the neck alone projecting above it. The arche- 

 gone originates from a superficial cell of the prothallium, which 

 divides by a tangential wall into an inner and an outer cell ; the latter 

 then develops, by further divisions, into the four rows of cells constitut- 

 ing the neck, which is, therefore, always comparatively short. The 

 inner cell puts out a protuberance between the neck-cells, which is first 

 of all separated as the neck-canal-cell, and below it a small portion is 

 again separated from the lower larger cell as the ventral canal-cell ; the 



1 These organs are frequently termed root-hairs ; but it is better to confine this 

 term to the epidermal appendages (trichomes) of the roots of Phanerogams and of the 

 sporophyte generation of Vascular Cryptogams, between which and true rhizoids there 

 is a functional rather than a morphological homology. 



