88 
interstices that the air, which leaves contain, seems to 
be lodged. In a leaf of fritillary (fritillarid) and of 
purslane (portttlaca\ small luminous points may be 
seen by the microscope, or even by the naked eye, 
which points are said to be produced by the light re- 
flected from the air contained in the utricular inter- 
stices. To prove this, he removed the pellicle of a 
leaf of fritillary, and cut the parenchyme, so that 
he could observe several of these luminous points; 
and then, by gently compressing the parenchyme 
under water to force out the air, he saw it issue 
in the form of bubbles, and the water, having 
taken its place, rendered the interstices transpa- 
rent, which were before opaque. In the petal of 
the rose, these inter-cellular spaces are very large ; 
and if the petal be slightly compressed under water, 
the air it contains will be seen to move with rapidity, 
following the different inflections of the utricular in- 
terstices*. 
325. But for the escape of the air thus lodged in 
the interstices of the parenchyme, some passages 
must exist, and these are to be found in the external 
pores. It has been much disputed among late writers, 
whether the leaves of plants are furnished with a 
proper and distinct epidermis. The late M. de Saus- 
sure considered what is called the epidermis to be 
composed of three different textures. M. Mirbel, 
however, denies its existence, and considers, what 
is so called, to be the union of the contiguous sur- 
faces of the external cells ; and M, Jurine, also, de- 
scribes this covering as formed by the exterior stra- 
Philos, Mag. vol. xvi. p, 109. 
