156 SYDNEY n. VINES. 



hyphse, have become incapable of active independent vegetation — 

 Stahl does not consider that the facts justify such a view. It is 

 true that the size of the algal cells which are left to vegetate 

 freely is, on an average, much smaller than that of the cells 

 which are acting as gonidia; but the rapid reproduction of the 

 freely vegetating Alga cannot co-exist with imperfect nutrition. 

 The differences in size and appearance must probably be attri- 

 buted solely to the various mechanical or physical conditions to 

 which the Algae are respectively exposed. 



Observations of a similar nature were made on Thelidhim 

 mimihdum (Korber). This Lichen made its appearance regu- 

 larly in the cultures of Endocarpon. It could not have made its 

 way thither by means of soredia, and the only means of account- 

 ing for its appearance is the assumption that it was produced 

 from spores which, on germinating, availed themselves of some 

 of the extruded hymenial gonidia of Endocarpon to form a 

 thallus. This assumption was proved true by direct experiment. 

 The spores of Thelidium sown in the absence of gonidia gave 

 rise to a mycelium which, so soon as the store of nutriment con- 

 tained in the spore was exhausted, withered away ; but if sown 

 with gonidia of Endocarpon a fructifying thallus was gradually 

 formed. In this case also the influence of the Fungus upon the 

 Alga was made apparent by the increased size of the latter, and 

 in the larger amount of chlorophyll contained within it. 



Further interesting facts were obtained by the investigation of 

 Poli/Uastia rugtdosa (Massal.)- The spaces between the asci of 

 this Lichen (each of which contains usually eight spores) are occu- 

 pied by hymenial gonidia arranged in rows, derived originally from 

 the gonidia of the thallus — from which they differ in a very 

 marked manner, the former being rod like, the latter more or less 

 rounded and dividing like the pieurococcoid gonidia of Endo- 

 carpon. If some of the thallus gonidia be cultivated on a slide 

 they will be seen to divide in successive planes in the three 

 dimensions of space. The products of this division are not, 

 however, rounded cells like those from which they are formed, 

 but are cylindrical and divide only in a plane at right angles to 

 their length, the segments separating the one from the other. 

 Thus it is possible to obtain from gonidia dividing like Pleuro- 

 coccus the algal form known as Stichococcus. This Stichococcus 

 is identical in form, in size, and in the mode of its division with 

 the rod-shaped gonidia occurring in the hymenium. 



As in Endocarpon so in Polyblastia, a certain number of 

 hymenial gonidia are extruded from the peritiiecium together with 

 the spore, which became invested by hyphse when the spore ger- 

 minates. The rod-shaped hymniial gonidia then gradually lose 

 their cylindrical form, increase in size and assume the rounded 



