ON THE CUTICLE OF PLANTS. 393 
cuticle are ascribable to a metamorphosis of the cellular 
membrane, which only takes place in the externally situated 
portions of the epidermal cells. 
Many slight deviations from this structure occur; some- 
times the substance of all the outer wall and lateral walls as 
far as they lie between the secondary coat exhibits the cha- 
racters of cuticle; e. g. Hoya carnosa ; sometimes a stratum 
of colourless matter (Membranenstoffes) lies on the inner 
side of the cuticular coats, as far as they constitute the outer 
wall and a portion of the lateral walls of the epidermal cells, 
as in Aloë obliqua; sometimes the inner colourless stratum 
covers all sides of the epidermal cells, and seems at first sight 
to form the whole wall of the cells, as in Arbutus unedo, 
(fig. 6); Cactus triangularis, and Viscum album ; sometimes 
the primary lateral walls of the cells are so far changed into 
the cuticular mass, as they are covered with a yellow secon- 
dary coat, as in the Aloé obliqua; sometimes this change in 
the primary lateral walls extends inwards further than that 
in the secondary coat, and therefore they enter between the 
uncoloured secondary lateral walls in the form of plates, as in 
Arbutus unedo. 
When the yellow mass which fills the outer portion of the 
cavity of the cell appears uniform, as in the cases just ad- 
duced, one is with difficulty convinced that one has to do 
with secondary membranes ; on the contrary, especially when 
- the uncoloured inmost coats form closed utricles as in 
Viscum, it is easy to imagine, that these unclosed membranes 
constitute the whole epidermal cell; and that the yellow or 
brown outer mass is a deposition external to the cells, in 
accordance with the views of Treviranus and Schleiden. f 
In these cases a proof that the yellow coats are deposited 
within, and not externally to the epidermal cells, is found in 
the presence of the primary wall of the cell upon the outer 
surface of the cuticle, as also in the circumstance that the 
Primary membranes of the lateral walls run through the 
cuticle to the outer coat. But inasmuch as this formation 
admits of another, though as I conceive a forced explanation, 
