328 MR. H. H. W. PEARSON ON THE 
position at a high angle, and therefore has a smaller illuminating 
and heating effect than on a horizontal leaf of the same area. 
Inthe following descriptions this position is denominated * semi- 
erect." 
Many leaves whose vernation is conduplieate never completely 
unfold, and the two halves remain more or less inclined to one 
another. Such a leaf receives the light- and heat-rays at a high 
angle, as in the case of the semi-erect leaf. 
In many cases the leaves or their parts move into a profile 
position and remain there while the sun is near the zenith. 
This movement is a direct effect of illumination (46), and is 
doubtless a means whereby the chlorophyll is proteeted from 
the effeets of intense light (47), rather than a method of 
regulating transpiration, although the latter may be to some 
extent influenced. Usually, leaves which show sun-movements 
are also subject to sleep-movements, although in some cases one 
form of movement was observed and not the other, which, in 
some cases at least, was almost certainly due to lack of opportunity 
of observation. Movements were observed in species of the 
following Natural Orders :—O xalidacez, Leguminos®, Euphor- 
biacew, and Graminex. For convenience of a brief description 
of the types of movement which were noted, the following four 
divisions will be used :— 
(1) Leaves whose sleep-position is the same as the sun-position ; 
i. e., the position assumed during the hours of most intense 
sunlight. This class includes three species, viz. :—Oxalis corni- 
culata, Crotalaria rubiginosa, and Phyllanthus simplex. In Oxalis 
corniculata the sun- and sleep-position assumed by the leaflets 
is well known in the genus as a sleep-position (48). The mono- 
phyllous leaves of Crotalaria rubiginosa rise up vertically until 
the ventral surface of the leaflet is in contact with the stem. 
This has been described by Thiselton-Dyer as a sleep-move- 
ment (49). In Phyllanthus simplex the small closely placed 
leaves move upwards towards the stem and close tightly 
upon one another in an imbricate manner, at night and in 
bright sunlight, as has been described by Massart for P. ovali- 
Jolius (50). 
(2) Leaves whose sleep-position differs from their sun- 
position. 
Biophytum proliferum.—In the sleep-movement the rhachis of 
the pinnate leaf sinks until it makes an angle of about 30? with 
