ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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perishing, owing to the absence in them of any water of constitution ; 
their moisture is always regulated by that of the substratum. In the 
dry state, or that of latent life, all the physiological processes proceed 
with great sluggishness. There is for each species an optimum of 
moisture, complete saturation not being the most favourable condition 
for the vital processes. The most favourable temperature is in general 
about 35° C. The injurious effect of too high a temperature appears to 
operate only on the process of assimilation, or rather, on the chlorophyll ; 
the protoplasm remains unaffected, and normal respiration proceeds 
even when assimilation has ceased. Low temperatures do not prevent 
the activity of respiration. Even at — 10° C. the process may be 
distinctly perceived. 
Thallus of Calcareous Lichens.* — Herr E. Bachmann divides cal- 
careous lichens into epilithic and endolithic. In the former the thallus 
is external to the calcareous substratum, and is differentiated into a 
cortical, a gonidial, and a medullary layer, the rhizoidal hyphae alone 
penetrating the substratum ; in the latter not only the rhizoidal, but 
also the gonidial and cortical layers are completely buried in the sub- 
stratum. Even the apotheces are first formed within it, and only break 
through the calcareous layer after they have attained a certain size. 
The algal cells of calcareous lichens are always collected into groups 
of various forms, either in roundish clumps or in small-celled rows. 
Each group of gonids is completely surrounded on all sides by a weft 
of mycelial hyphae; they may or may not contain oil. The cortical 
zone of endolithic calcareous lichens is always composed of two kinds 
of hyphae, distinct, or collected into balls. The rhizoidal portion con- 
sists of a weft of hyphae, denser towards the surface, looser within ; 
spheroidal cells occur in most species. The rhizoidal portion of epi- 
lithic calcareous lichens resembles in all points that of the endolithic, 
and usually also contains spheroidal cells, and occasionally a few 
scattered gonids. The observations were made on fourteen species of 
endolithic, and five of epilithic lichens. 
In contrast to the calcareous, siliceous lichens have a very strongly 
developed thallus ; but, on the other hand, the rhizoidal portion is less 
developed. 
Siphulastrum.t — Sig. A. Jatta has studied this alpine genus of 
lichens from Terra del Fuego, and considers that it belongs to the 
Siphulei, differing from the other genera of this family in having a 
cyanophyceous alga-constituent ( Scytonema ), and specially adapted by 
its habit for an alpine habitat. In the complete absence of apotheces, 
the following is proposed as a diagnosis of the genus : — Thallus den- 
droideus, ramosus, v. dichotome divisus ; rami firmi, plus minusve teretes, 
undique corticati, aggregati, tantum ad apices ochroleuci, inferne 
ustulato-nigri ; hyphae densae, contortae, breviter articulatae, haud 
longitudinales ; gonidia scytonemea ; apothecia ignota. 
New Marine Lichen4 — Mr. G. Massee describes a new marine 
lichen, Verrucaria Isetevirens , found on smooth rocks between tide-marks 
on both coasts of Scotland. 
* Ber. Deutsch. Bot. Gesell., x. (1892) pp. 30-7 (1 pi.). 
f Bull. Soc. Bot. Ital., i. (1892) pp. 246-50. 
J Journ. of Bot., xxx. (1892; pp. 193-4 (1 pi.). 
