204 PRACTICAL BOTANY. 



to maturity. Note especially in such sori tlie following stages of 

 development : 



i. A simple, hair-like process, consisting of a single cell, or of 

 two separated by a transverse wall. 



ii. The upper cell divided up so as to consist of a central 

 tetrahedral cell (archespore), surrounded by a single layer of 

 cells, which form the wall. 



iii. The central cell or archespore is divided into 



. One cell, or a group of cells, lying centrally, which gives 

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

 themselves. 



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

 are ultimately absorbed. 



B.THE OOPHORE. 



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, p. 16. 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 previously been 

 sown : by this means a series of preparations illustrating the 

 various stages of development of the prothallus may be obtained. 

 Note in such a series of preparations, under a low power 



1. The bursting of the outer coat of the spore, and the protru- 

 sion of the inner coat through the slit. 



