Fink: Classification of Lichens 
]35 
lichen hyphae and the trichogynes. His observations with dry 
sections in glycerine were also extended to many foliose and fru- 
ticose lichens with similar results ; and he concluded that the thalli 
of lichens are richly provided with means for aeration. 
It will be noticed that all of the means for aeration enumer- 
ated above are not real canals but loose passages between en- 
tangled hyphae, and that most of them are accidental or occa- 
sional. We have taken pains to confirm Zukal’s observations 
upon the air content of dry sections in glycerine and find the air 
bubbles in lines and spots. The glycerine treatment then proves 
the presence of air in lichen thalh. The occurrence of thin places 
in cortices, the soralia, the cyphellae, the empty spenuagones, the 
hollow cylinders, the crude canals and other makeshifts are a 
matter of common knowledge among students of lichen anatomy. 
But after all this is admitted, we are still not convinced that suf- 
ficiently rapid air movements and the means for sufficient aera- 
tion of the algal hosts in lichens are present. These hosts have 
greater need for aeration than the lichen itself, which needs air 
only for respiration, while the alga could use it also for carbon 
assimilation. Furthermore, the air enters through openings in 
the tissues of the lichen, which is reached directly, while many 
of the algal host cells are reached only by a slow circuitous route 
downward or upward through the cortex, thence through or 
along the hyphae of the medulla. We are of the opinion that 
nothing but definite air canals, leading directly from the ex- 
terior to all the algal groups within the lichen, could accomplish 
aeration for these algal cells in an efficient manner. 
Schneider’s results (m), obtained during the time that Zukal 
was working, add little to those of the latter worker. Schneider 
observed algae extending almost tp the upper surface, in circum- 
scribed areas, in lichen thalli which had thick cortices elsewhere 
than in these areas. He also saw, in certain lichen thalli, intra- 
cellular spaces passing from some of the algal clusters through the 
cortex and the epidermis to the exterior, taking a circuitous in- 
stead of a direct route, and often following almost a horizontal 
course in the epidermal layer. He found these crude canals 
closed when the thalli were dry. His statements read quite as 
convincingly as those of Zukal, but we can not accept the results 
