194 



larly Ihose of the undermost pari of the frond, often contain a great quantity of 

 starch grains taking a brownish colour on treatment witli iodine. 



Old crusts are often composed of several crusts growing one over the other. 

 This is principally caused, as in the foregoing species, by the cessation of growth 

 of great parts of the fronds, particularly those which have produced nemathecia, 

 while in other parts the erect filaments continue growing in the next season, giving 

 rise to a new frond growing in a horizontal direction over the old frond, and this 

 may be repeated several times, so that old fronds may be composed of 6 or more 



Fig. 115. 



CrtioricUa Didnii. A, marginal jiart of frond in vertical section. B, inner part of frond in vertical section. 

 C, marginal part of frond seen from above. A and D, 295:1; C, 215:1. 



distinct crusts. The under side of fronds or lobes thus produced is usually rather 

 irregular (fig. 115 A). Overlapping, though in a smaller degree, may also take place 

 in the border of the frond, where the lobes sometimes grow over one another, and 

 the same may occur on the meeting of two of the fronds produced in the manner 

 first described. A formation of superposed fronds by horizontal splitting, as described 

 for Cr. Nordstedtii by Mrs. Weijer-van Bosse may also occur (see above p. 189). 



The sexual nemathecia are cushion-shaped, of various extent. The antheridia 

 occur in particular nemathecia or interspersed in the female ones. As shown by 

 KucKuciv (1. c. lig. 18) the spermatangia arise by transverse and longitudinal divisions 

 of the cells of the nemathecial filaments (fig. 116 A). 



The nemathecial filaments of the female nemathecia are of equal thickness 

 in their whole length, and consist at the stage of fertilization of about 5 cells, 



