274 MOSSES AND FERNS chap. 



The Gametophyte 



The germination of the spores and development of the 

 prothalHum were first investigated by Luerssen (5) and Jonk- 

 man ( i ) in Angiopteris and Marat tia, and later by the latter 

 investigator for Kaulfiissia (2). More recently Brebner (i) 

 has described the prothallium and embryo in Dancra. 



The spores are of two kinds, bilateral and tetrahedral, but 

 the former are more common. They contain no chlorophyll, 

 but oil is present in drops of varying size, as well as other 

 granular bodies. The nucleus occupies the centre of the spore 

 and is connected with the w^all by fine protoplasmic filaments. 

 The wall of the spore is colourless and shows three coats, of 

 which the outer one (perinium) is covered with fine tubercles. 



Germination begins within a few days and is first indicated 

 by the dcA^elopment of chlorophyll. This does not, as Jonkman 

 asserts, first appear in amorphous masses, but very small, 

 faintly-tinted chromatophores are present between the large oil- 

 drops, and rapidly increase in size and depth of colour as ger- 

 mination proceeds, their number increasing by the ordinary 

 division. In the bilateral spores the exospore is burst open 

 above the thickened ventral ridge found in these spores, and the 

 growing endospore slowly protrudes through this. The spore 

 enlarges to several times its original diameter before the first 

 division occurs, and forms a globular cell in which the large 

 chloroplasts are arranged peripherally. 



- The first division takes place about a month after the spores 

 are sown, and is perpendicular to the longer axis of the cell, 

 dividing it either into two equal parts, or the lower may be 

 much smaller and develop into a rhizoid. In the former case 

 each cell next divides by walls at right angles to the first, and 

 the resulting cells are arranged like the quadrants of a circle, and 

 one of these cells becomes the two-sided apical cell from which 

 the young prothallium for a long time grows (Fig. 149), much 

 as in Aneiira. This type of prothallium, according to Jonkman, 

 is commoner in Marattia than in Angiopteris^ w^here more com- 

 monly a cell mass is the first result of germination. This latter 

 is usually derived from the form where a rhizoid is developed 

 at first. In this case only the larger of the primary cells gives 

 rise to the prothallium. In the larger cell, divisions take place 

 in three directions and transform it into a nearly globular cell 



