166 W. Watson. 
filifonne v. juliforme, B. ccespiticium v. imbrication, Weisia viridula 
v. densifolia, Cynodontium Wahlenbergii v. compaction (on the higher 
Grampian rocks), Fissidens adiantioides v. collinus, Polytrichum 
commune v. minus, Cathariuea undulata v. minor, C. Crispa v. 
densifolia, Dicranella cerviculata v. pusilla, Dichodontium pellucidum 
v. compaction, Philonotis fontana v. compacta, Sphagnum cymbifolium 
v. congestion, S. papillosum v. confertum, Plagiochila asplenioides v. 
minor, P. punctata v. minuta, Gymnocolea inftata form compacta 
(/. /riA'rt and f. natans are lax forms of wet places), Bazzania 
triangularis (form of drier ground) Madotheca rivularis v. faroensis, 
Cephalozia bicuspidata v. conferta, Lepidozia replans v.julacea. 
(2) Investments of Dead or Non-Chlorophyllous Cells. 
These protect the underlying chlorophyllous cells from too 
great evaporation. 
(a) Hyaline Hairs or Hyaline Apices of the Leaves. These are 
especially characteristic of tufted bryophytes, which often have a 
white appearance in dry weather since the non-chlorophyllous cells 
are the only ones exposed. In this way the active chlorophyllous 
cells are screened from the drying action of the wind and from the 
too powerful rays of the sun. Hyaline hairs are present in many 
species of Grimmia (Fig. 3, 1, 2) Rhacomitrium, Pottia, Tortula 
(Fig. 3, 3-6, 12) Campylopus, Bryum and Polytrichum. They may 
be formed by the excurrent nerve as in Tortula muralis, Pottia 
criuita, Bryum inclination, and Campylopus introdexus, or simply by 
the apical cells of the finely-pointed leaves becoming non- 
chlorophyllous, as in Hedwigia ciliata, Funaria calcarea, Hylocomium 
splendens, Coscinodon cribrosus, Eurynchium cirrosum, E. piliferum, 
Orthotrichum diaphanum, and species of Grimmia and Rhacomitrium, 
The apex of the leaf is hyaline, but is not usually prolonged into a 
fine point in Bryum argenteum, Grimmia apocarpa, G. torquata, 
G. elongata, and in species of Gymnomitrium. 
That this hyaline leaf-apex is a xerophytic arrangement is 
shown by the fact that many bryophytes displaying this peculiarity 
have varieties or forms of moister or shadier ground in which it is 
absent, whilst it is accentuated in forms of drier situations. The 
long hair-point is shorter or absent in forms of Tortula muralis 
growing on moist walls (Fig. 3, 6, 7), the var. aestiva of shaded rocks 
also having a short point. The hyaline points of Grimmia apocarpa, 
vars. rivularis and gracilis, Rhacomitrium heterostichum vars. 
alopecurum and gracilescens, R. canescens v. ericoides, are shortened 
