120 The Botanical Gazette. [April 
In Dawsonia superba, a new Zealand relative of Polytrichum, 
instead of a single hypoderm bundle, there are generally three 
arranged radially, increasing in differentiation as they ap- 
proach the exterior. The origin of the hypoderm bundles is 
thus plain. Their first elements arise by differentiation of 
cells of the pericyclic sector, 7. ¢., the bundles are of internal 
origin. The remaining elements are added from the hypo- 
derm by the differentiation of its cells. 
The relation of the peculiar triangular radial symmetry of the 
subterranean stem to the circular symmetry of the aerial stem 
is worked out and the transition described. The sectors and 
bundles of the angles extend laterally until adjacent ends 
meet and at the same time the radial extension diminishes 
thus gradually bringing the radial arrangement into the con 
centric ; 
The more important physiological results are here sum — 
marized. 
When an aerial moss (Polytrichum juniperinum was used) 
is subjected to an aquatic life, the epidermal layer of the stem 
and leaf is profoundly modified. The size of the cells is 
larged, the cuticle disappears and the slightly thickened wal 
retain a cellulose nature. The leaf loses its chlorophyllose 
lamella, the limb is reduced and the form slightly modified: 
f the mosses are grown in air or in water, and the cone 
tions of light and the orientation of the stem are varied, the 
stems are found to be very feebly negatively geotropic, 
strongly positively heliotropic. Heliotropism is ue fet 
ally to those at the summit. The cause of the ne 
found in the contraction aud the turgescence of chee 
membranes of the leaf. 
In both the open and the closed condition mosse 
darkness, evolving CO, and absorbing O; the ré 
S respite in 
tsi 
lose 
jation PY 
