280 Yapp. — On Stratification in the Vegetation of a 
low, compact growths, which are sheltered by their position (cf. p. 298) 
though not directly by other plants. Thus Hydrocotyle , when growing in 
rank vegetation, forms erect petioles, often a foot or more in length. 
When growing, however, on (say) an exposed mound of peat, the petioles 
remain short, and on reaching the surface of the soil bend horizontally, and 
tember.) x 
so place the laminae close to the ground (cf. Text-fig. 2). This behaviour 
of Hydrocotyle can be compared to that of many rosette-forming plants. 
The leaves of the latter may vary from a horizontal to a more or less erect 
position, according to the height of the surrounding vegetation. It is 
probable that in these cases relative humidity plays a very important part 
in determining the proper position for the leaves (cf. p. 298). 
shade plants. He sought to connect these similarities with reduced transpiration ; due to relatively 
great air and soil moisture (p. 200). 
