BY JOHN SHIRLEY, D.SC. 57 



melia, and for the ecypliellate Stictas by the absorption 

 pores. (Plate V., fig. 7.) 



The Pai'melias grow on rocks, fences and trees, and 

 apply themselves close to the surface to which they are 

 usually attached by rhizoids. The upper surface is 

 usually more heated than the under surface, while the rain 

 water, absorbed by ths^ substratum, is in contact with the 

 lower cortex. The capillary tubes already described, 

 Avhich can give off excess of moisture as vapour from the 

 upper part of their water column, will be replenished from 

 below as long as the suppl}' continues, inorganic salts will 

 be supplied to the alga, and saprophytic matter absorbed 

 by the fungus. 



A living specimen of Parmelia tiliacea, Ach., whose 

 upper surface was examined in reflected light under a low 

 power. (90 diameters), showed the pores as shallow pits, 

 lighter in colour than the other parts of the thallus but 

 closed. The plant (symbiotic) structure has tlierefore the 

 power of closing the pores, but these are always open 

 in tlialli killed by chromo-acetic mixtures. 



That these pores, as also the cyphellse of the Stictaceae, 

 are not breathing pores only, seems certain from the facts 

 already stated, as also from their position. In higher 

 plants, when the lower surface cf the leaf, the part 

 usually provided with stomata, floats on water, the breath- 

 ing pores are on its upper surface. In Anthoceros so- 

 called stomata are found on the lower surface of the 

 thallus, but their function is to secrete mucilage, and, as 

 Goebel states, they are better named as mucilage pits. In 

 Marchantia the pseudo-stoaiiata are all in the upper cor- 

 tical layer and not in the cortex that rests on the sub- 

 stratum. That the cyphellae, and their offspring the 

 absorption pores, should function as breathing pores only, 

 and be placed en the surface closely attached to the bark 

 or rock, 'is possible, but is unusual in the plant world. 

 It must also be remembered that the pores can be closed 

 above, but are open below, certainly in those species with 

 hollow rhizoids. 



To ascertain the true purpose of the cyphellae of 

 lichens, and of the absorption pores which are believed to 

 be derived from them, the following experiments were 

 made' — the plant chosen being Heterodea ?nii fieri, Nyl., 

 selected on account of its terrestrial growth. The plants 

 were gathered with a sufficient quantity of the soil of the 

 substratum to prevent injury to the rhizina^. 



