104 
Review 
Polychidium muscicolum and Leptogium micvoscopicum seem very similar, 
though those of the former are given as Scytonema, and those of the 
latter as Nostoc. Figures of the algal symbionts are given from the free 
algae. It would have been better if illustrations of the actual gonidia 
had also been given, since a young lichenologist may be led to expect to 
find algal symbionts in the lichen like those figured. 
Many instances of what various workers have called saprophytism 
and parasitism are mentioned. Some of the so-called saprophytes 
amongst lichens are no more entitled to the name than are radishes from 
a well-manured garden plot, and some of the examples of parasitism are 
scarcely more so than when plantain smothers other plants and feeds 
on the derived humus; others, in which digestive action precedes the 
actual covering of the host, are better examples. Malme’s view (quoted 
on p. 261) that “ Buellia vervuculosa and B. czthalea may be living on the 
thallus of Rhizocavpon distinctum with which they are constantly asso¬ 
ciated,” is not supported by the distribution of these lichens in the 
British Isles. When Miss Smith expresses her own views on these so- 
called parasitic and saprophytic lichens, they are generally of a sceptical 
or qualifying nature, though it is not always easy to perceive how far 
she agrees with the work and views she gives an account of. 
The colour of lichens has an excellent section devoted to it, and the 
effect of light on this colour is referred to in another section of the chapter 
dealing with physiology. The darkening or deepening of the colour is 
attributed to the influence of light. In some lichens it may not be the 
only factor, the lack of water and nutriment may also contribute to the 
darkening. The dark colour of such plants as Rhizocavpon confevvoides, 
Buellia impressula, and Lecidea latypea on shingle, is due to the pre¬ 
dominance of the hypothallus, the nutrition being deficient for the proper 
formation of the thallus. The change in the colour of the apothecia 
(p. 245) is of frequent occurrence, and sometimes is well marked where 
a number of stones have lain heaped together for many years. The 
apothecia on the illuminated portion may be very dark whilst those 
which are shaded are pale in colour. The darkening of old apothecia, 
e.g. Candelaviella vitellina, may be due to decomposition products. 
Those who uphold Church in his views of a direct evolution of lichens 
from algae, may derive some consolation from the following passages, 
when isolated from their contexts. “In Verrucavia mucosa... and in 
some other sea-washed species the arrangement of the tissue elements 
recalls that of crustaceous Florideae such as Hildenbrandtia, Cruoria, 
etc.” (p. 73). “ Mechanical tissue scarcely appears among fungi ” (p. 105). 
“These attaching sheaths (of Usnea, etc.)...may be more truly compared 
with the primary thallus of the red algae, Dumontia and Phyllophora, 
which are similarly affixed to the substratum” (p. hi). “Such a view 
might be possible if we could regard lichens and Florideae as derived 
from some common ancestor” (p. 179). “The hyphae travel in the sheath 
alongside the cel]-rows and the symbiotic plant retains the tufted form 
of the alga as in Lichina with Rivularia, Leptogidium with Scytonema, 
and Ephebe with Stigonema” (p. 284). In the phylogenetic chapter, 
and more definitely in an appendix, Miss Smith opposes these views, 
and in so doing voices the opinions of lichenologists in general. Even 
those who have seen “ the shaggy covering of Lichen on the cliffs facing the 
Atlantic ”(“ The Lichen as Transmigrant,” J. ofBot. 1921, p.45) find little 
evidence in support of Church’s views and much in conflict with them. 
A large amount of space is given to Zahlbruckner’s method of classi¬ 
fication. The appreciation given to it is well deserved, as it is the most 
natural and thorough grouping of the lichens which has been attempted. 
Miss Smith’s lucid description brings it within the range of every British 
student. Some desirable information has been omitted, probably owing 
