72 BOTANICAL GAZETTE [JANUARY 
and their general agreement on similar although widely separated areas tend to 
show that they represent successive changes in the vegetation due to climatic 
changes during the passing away of the Glacial period. None of the districts 
investigated show any remains of arctic plants at the base of the peat; but some 
of them, on the contrary, contain remains of hazel in the basal layer. As an 
illustration of sequence, that of the Galloway peat is as follows: (1) birch forest 
(lower buried forest), (2) arctic plant beds, (3) pine forest (upper buried forest). 
The evidence seems to give support to the view that the later phases of the Glacial 
epoch were separated by somewhat long genial interglacial periods. The details 
given in the two Siti and well illustrated, are full of interest to students of the 
succession of flora 
the Highlands the peat deposits are divided into two groups: (1) those 
of sie western districts, possessing no arctic plants at the base, but a forest bed 
(Betula and Corylus), overlaid by plants indicating wet moorland conditions; 
and (2) those of the northern and northeastern districts, possessing only one 
well-marked forest bed, and with an arctic plant bed at the base of the peat.— 
Geophilous species of Peperomia.—Hi11"° has been investigating the peculiar 
geophilous species of Peperomia, his attention having been called to them during 
travels in the Andes of Bolivia and Peru. These species form a comparatively 
small section of a large genus, having corms or tubers or rhizomes, which seemS 
to be correlated with the possession of more of less peltate leaves. Detailed 
descriptions of the seedlings of the different species serve as an introduction to 
general discussion and conclusions. In these forms the cotyledons exhibit a 
remarkable division of labor, one remaining within the seed and serving as an 
absorbing organ, the other becoming aerial and green. From this fact as a 
start, HILL sees change of function of one of the cotyledons gradually leading 
into the monocotyledonous condition. The large conclusion is the origin of the 
monocotyledons from dicotyledons, as held by Miss ErHet SarGant, but the 
method is different. Miss SARGANT sees the origin in a phylogenetic fusion 
of the two cotyledons; while Hrxt sees it in the change of function of one of the 
aerial cotyledons to an absorbing organ. While Miss SARGANT traces the con- 
nections between Ranunculaceae and Liliaceae, Hitt traces them between 
Piperaceae and Araceae. The Piperaceae are certainly very primitive dicoty- 
ledons, and the Araceae are the most Dicotyledon-like of the monocotyledons; 
and the transition from the geophilous species of Peperomia to those of Arisaema 
seems quite plausible. However, such discussions as yet are only suggestive 
of further investigations; and it is conceivable that there may have been more 
than one way of passing from the dicotyledonous to the monocotyledonous con- 
dition.—J. M. C. 
10 Hirt, ArtHUR W., The morphology and seedling structure of Peperomia, 
together with some views on the origin of Monocotyledons. Annals of Botany 20: 
395-427. pls. 29-30. 1906. 
