Suberin and Cutin 
27 
These substances consist of aggregates of organic acids, the 
suberogenic (or cutinogenic) acids, which are present to a small 
extent as glycerides or true fats, to a greater extent as condensation 
products or anhydrides of the acids. The differences between the 
suberin and the cutin of different plants, or between these two 
substances within the same plant will be due, in part to differences 
in their constituent acids, and in part to differences in the external 
and internal conditions prevailing whilst these acids pass over into 
the form that they assume in the mature suberin or cutin lamella. 
A consideration of the work described above indicates many 
avenues of research opening before the investigator. On the one 
hand, only extended observation in which macro-chemistry and 
micro-chemistry both take their share can put the detailed knowledge 
of suberin and cutin on a broad basis, and until that is done the view 
outlined above, however satisfactory as an explanation, cannot be 
regarded as having a sufficient experimental basis. 
On the other hand questions are suggested as to the methods by 
which the original lamellae of suberin and cutin were formed. The 
acids described here as suberogenic are too empirically known yet 
to permit an elucidation of their constitution, though presumably 
they will readily admit of chemical derivation from some of the 
carbohydrates found within the plant (though by no means neces¬ 
sarily from celluloses). 
The origin of the suberogenic acids has to be traced, and then we 
have to ascertain under what conditions in the plant these substances 
can assume the impermeable form, insoluble in fatty solvents, in 
which they are present in the mature suberin or cutin lamella. 
These conditions will be different from the methods of heating in 
sealed tubes adopted by Gilson and are probably already indicated 
by some of the literature referring to the conditions under which 
cork walls and cuticle are formed. It is for example very fascinating, 
in the light of the views expressed above, to read such a summary 
as that provided by Kuster (12) of the conditions under which wound 
cork is formed, and to see that some conditions favour the early 
and extensive deposit of suberin on the cell arising from the newly 
formed meristem, whilst other conditions appear to impede its 
formation. 
SUMMARY 
1. Suberin is the name given to a substance present in the 
median lamella of the wall of periderm cells, between the middle 
lamella outside and the cellulose layer within; to this substance the 
