350 MALE FERN. 



strain thus set up makes the ring straighten itself out and 

 become curved in the opposite direction, the sporangium- 

 wall being torn open below the end of .the ring. 



491. The development of the Fern sporangium can be 

 readily followed in sections through young sori, since in the Male 

 Fern (as in all the commoner British Ferns) sporangia of all ages 

 are mixed together in the same sorus. The fertile leaf of the 

 Hartstongue is especially useful for this purpose, since successive 

 sections can be made across the long sori. 



The superficial cell of the placenta which is about to form a 

 sporangium grows out and divides into an upper capsule-forming 

 cell and a lower stalk-forming cell. The former divides by 

 three curved intersecting walls, cutting out an inner pyramidal cell 

 (apex pointing downwards) from three outer cells, then the inner 

 cell divides by a curved transverse wall, so that we have now a 

 central pyramidal cell enclosed by four outer cells, which are to 

 form the wall of the capsule. The stalk-cell divides by both trans- 

 verse and longitudinal walls, giving rise to two or three rows of 

 cells. 



Returning to the capsule, the central cell now divides by four 

 walls parallel to those first formed, so that within the wall-layer 

 there is now a tapetum, or tapetal layer, of four cells, which 

 undergo further division and are ultimately used up in the nutrition 

 of the spore-forming cells. The latter are produced by repeated 

 divisions of the central cell (archesporial cell or archesporium) 

 to form a mass of (usually twelve in Male Fern) spore mother- 

 cells, each of which divides later into four spores, after the nucleus 

 has divided into four. 



The wall-forming cells divide only by vertical walls, hence the 

 wall remains one layer of cells, but the tapetum usually divides 

 into two layers ; eventually the spore-mother-cells separate from 

 each other, they float in mucilaginous liquid formed by disintegra- 

 tion of the tapetal cells. 



In Hartstongue each of the (usually sixteen) spherical mother- 

 cells divides by walls between the four nuclei (formed by division of 

 the mother-cell nucleus) in such a way that each spore is tetrahedral, 

 with three flattened sides (where it was in contact with its three 

 sister- spores) meeting at a point (the centre of the mother-cell) and 

 a curved outer side ; in Male Fern the mother-cell is divided by 

 walls at right angles, so that each young spore is the quarter, or 

 quadrant, of a sphere, but later it becomes bean- or kidney-shaped. 



492. Cultivation of Fern Frothalli. Failure of prothallus 

 cultures is generally due to invasion by fungi, but this can be largely 

 obviated by sterilising the vessels and the soil used. Collect the 

 spores on pieces of paper, or in envelopes, by simply cutting off 

 fertile leaves and allowing them to dry on the paper, which will 



