95 
similar conclusion from a study of the external forms of 
these scars. The question has been set at rest through the 
discovery, by Mr. D’Arcy Thompson of Edinburgh, of two 
specimens in which the cones are preserved in connection 
with the scars. Each cone was obviously developed from a 
leaf-covered bark, but as it grew in diameter its truncated 
base pressed down the neighbouring leaves and thus pro- 
duced the well-known large circular areola. The actual 
organic connection of the cone and its parent branch was 
obviously limited to a small circular areola in the centre of 
each scar. After these deciduous strobili fell, the scars 
remained permanently impressed upon the bark of the tree. 
At first each scar was small and circular, but as the stem 
enlarged both in length and diameter the scars underwent 
a similar enlargement ; but since the longitudinal growth 
of the stem was obviously more rapid than the transverse 
one, it necessarily resulted that these originally circular 
scars became converted into vertically elongated oval ones. 
This change in the shape of leaf-scars resulting from the 
direction of growth is well shown in the arborescent stems 
of living species of Alsophila. Ulodendron therefore was a 
branching Lepidodendroid plant whose branches supported 
distichously arranged strobili, the individuals of the two 
series being disposed alternately. 
