ASPIDIUM GAMETOPHYTE 311 



Note especially in such sori the following stages of develop- 

 ment : 



i. The sporangium appears as a simple, hair-like process, 

 consisting of a single cell, or of two separated by a transverse wall. 



ii. The upper cell divides so as to consist of a central tetrahedral 

 cell (archesporium), surrounded by a single layer of cells, which 

 form the wall. 



iii. The central cell or archesporium is divided into 



a. One cell, or ultimately a group of cells, lying centrally, 

 which give rise to the mother-cells of the spores, and finally, 

 by division of each mother-cell into four, to the spores them- 

 selves. 



b. A layer of transitory tapetal cells, which surround a, and 

 are ultimately absorbed. 



B.THE GAMETOPHYTE, OR OOPHYTE. 



I. Dry some of the leaves of the Male Fern, which 

 bear sori, on a piece of paper : the spores will then be set 

 free by the rupture of the sporangia, and they may thus 

 be collected in large quantities/ Sow some of them on 

 damp earth : keep them moist, and sheltered from direct 

 sunlight ; they will then germinate, and after a few 

 weeks the surface of the soil will be found to be covered 

 with small, green, flattened bodies, each of which is an 

 individual prothallus. 



If it be desired to follow the germination of the spore, and the 

 first stages of the development of the prothallus in detail, the 

 spores may be placed in a hanging drop in a moist chamber, as 

 described in Appendix A. But for all ordinary purposes it will 

 suffice to pick off young prothalli, from time to time, with a 

 needle, from the surface of the soil on which spores have pre- 

 viously been sown : by this means a series of preparations illus- 

 trating the various stages of development of the prothallus may 



