380 DEVELOPMENT OF PROTHALLIUM OF FERNS. 



Thecae, usually have a somewhat angular form, and are invested by 

 a yellowish or brownish outer coat, which is marked very much in 

 the manner of Pollen-grains (Fig. 230) with points, streaks, ridges, 

 or reticulations. When placed upon a damp surface, and exposed 

 to a sufficiency of light and warmth, the Spore begins to ' germi- 

 nate,' the first indication of its vegetative activity being a slight 

 enlargement, which is manifested in the rounding-off of its angles ; 

 this is followed by the putting-forth of a tubular prolongation (b, a) 

 of the internal cell-wall through an aperture in the outer_ spore- 

 coat ; and by the absorption of moisture through this root-fibre, 

 the inner cell is so distended, that it bursts the external unyielding 

 integument, and soon begins to elongate itself in a direction oppo- 

 site to that of the root-fibre. A production of new Cells by sub- 

 division then takes place from its growing extremity : this at first 

 proceeds in a single series, so as to form a kind of Confervoid fila- 

 ment (c) ; but the multiplication of cells by subdivision soon takes 

 place transversely as well as longitudinally, so that a flattened 

 leaf- like expansion (d) is produced, so closely resembling that of a 

 young Marchantia as to be readily mistaken for it. This expan- 

 sion, which is termed the Prothallium, varies in its configuration 

 in different species ; but its essential structure always remains the 

 same. From its under surface are developed not merely the 

 root-fibres (a, b) which serve to fix it in the soil and at the same 

 time to supply it with moisture, but also the Antheridia and 

 Archegonia which constitute the true representatives of the essen- 

 tial parts of the flower of higher Plants. — Some of the Antheridia 

 may be distinguished at an early period of the development of the 

 Prothallium (A, h) ; and at the time of its complete evolution these 

 bodies are seen in considerable numbers, especially about the 

 origins of the root -fibres. Each has its origin in a peculiar pro- 

 trusion that takes place from one of the cells of the Prothallium 

 (Fig. 194, A, a) : this is at first entirely filled with chlorophyll 

 granules ; but soon a peculiar free cell {b) is seen in its interior, 

 filled with mucilage and colourless granules. This cell gradually 

 becomes filled with another brood of young cells (e), and increases 

 considerably in its dimensions, so as to fill the projection which 

 encloses it : this part of the original cavity is now cut off from that 

 of the cell of which it was an offshoot, and the Antheridium hence- 

 forth ranks as a distinct and independent organ. Each of the 

 Sperm-cells (b, e) included within the antheridial cell, is seen, as 

 it approaches maturity, to contain a spirally-coiled filament ; and 

 when they have been set free by the bursting of the antheridium, 

 the sperm-cells themselves burst and give exit to their Anthero- 

 zoids (c), which execute rapid movements of rotation on their 

 axes, partly dependent on the six long cilia with which they are 

 furnished. — The Archegonia are fewer in number, and are found 

 upon a different part of the Prothallium. Each of them at its 

 origin presents itself only as a slight elevation of the cellular layer 



