MARCHANTIA. SPOROPHYTE 377 



spirally thickened elaters, and the consequent separation 

 and scattering of the spores. 



Sections should also be cut through female receptacles of various 

 ages, and by a comparison of these the development of the 

 sporogonium may be traced from the first divisions of the fertilised 

 ovum to the mature condition. 



For comparison with those of Marchantia the sporogonia of 

 Pellia should also be examined. Cut median longitudinal 

 sections of a thallus of Pellia., so as to traverse a young 

 sporogonium of such age, that its round head may just be 

 seen projecting from the pocket (see p. 362) : this is the 

 condition of the sporogonia during the winter, for those which 

 are the result of fertilisation in the early summer of one year 

 do not scatter their spores till the spring of the year following. 

 In such sections observe 



1. The thallus which bears the sporogonium, while round 



the sporogonium may be recognised 



a. An outer protective flap on either side : this 



is the involucre. 



6. The more or less complete remains of the 

 calyptra, which is developed from the wall 

 of the archegonium, and may still cover the 

 sporogonium completely. 



2. The sporogonium, consisting of '- 



a. The seta, with its enlarged triangular foot, by 

 which it is inserted on the tissue of the thallus ; 

 the upper part of the seta is cylindrical, and is 

 composed of rows of narrow discoid cells, with 

 much starch : it is the enlargement of these 

 cells which brings about the extension of 

 the seta. 



&. The head of the sporogonium, which consists of 

 a wall composed of two layers : this surrounds 

 the spherical mass of spores and elaters. Note 



