312 PRACTICAL BOTANY 



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. 



2. The formation of 



. An aerial portion, containing chlorophyll, and undergoing 

 repeated cell-divisions, which result in the development of a 

 flattened, roughly triangular, expansion. 



b. A root-hair, which remains undivided, does not contain 

 chlorophyll, and grows downwards into the soil. 



3. In older prothalli of the series note an incurving of the 

 margin of the part more remote from the original spore : this is 

 due to the slower growth of that part and the more rapid growth 

 of the lateral parts : at the base of this depression is one wedge- 

 shaped apical cell, from which segments are cut off alternately 

 on opposite sides. The identity of the apical cell and regularity 

 of the segments are lost in the later stages of development. 



II. Examine a single, fully-grown prothallus with 

 the naked eye, and observe 



1. The form, which is flattened, and more or less 

 kidney-shaped, with a depression of the margin, at the 

 base of which is the organic apex of the prothallus. 

 Note that the central part of the prothallus is often 

 perceptibly thicker than the periphery : this thicker 

 part is called the cushion. 



2. The position of the prothallus while growing : 

 it is usually oblique to the surface of the soil. 



3. The root-hairs, which spring from the under 

 surface of the cushion, and run downwards into the 

 soil. 



4. The green-colour, due to the presence of chloro- 

 phyll: the prothallus is thus capable, under suitable 

 circumstances, of carrying on the process of elaboration 

 of fresh organic substances. 



