24 
J. H. Priestley 
Van Wisselingh tried all these methods on the tissues of certain 
selected plants and compared carefully the widely differing results 
he obtained. It would take too long to show how, by careful com¬ 
parison of one series of results with another, he gradually arrives at 
conclusions as to the nature of the suberin or cutin in the particular 
plants under investigation, conclusions which seem to the present 
writer very critically established. 
We must confine ourselves to two general conclusions of van 
Wisselingh’s, first that the suberin lamella has no basis of cellulose, 
secondly that the suberin and cutin are not definite substances but 
varying aggregates. 
Van Wisselingh, repeating von Hohnel’s observation that the 
suberin lamella during treatment with potash began to give staining 
reaction with iodine and sulphuric acid or with chlor-zinc-iodine, 
had already published ( 16 ) his reasons for doubting whether this 
reaction could be due to cellulose. Gilson later published his paper, 
describing the isolation of phellonic acid (see p. 21) and showed that 
both phellonic acid and its salt gave red to red-violet coloration with 
the iodine reagents used and suggested that von Hohnel had been 
misled by the production of phellonic acid during the saponification 
of the suberin by potash. Van Wisselingh then returned to the 
subject( 17 ); he showed that the 'coloration with iodine during treat¬ 
ment of the lamella with potash is a transient phenomenon, whilst 
cellulose would remain during this treatment; he further showed 
that after complete removal of the suberin, either by heating to 
300° C. in glycerine or by saponification in 10 per cent, alcoholic 
potash or 10 per cent, glycerine potash, the suberin lamella gives no 
trace whatever of cellulose, and he gave further reasons for thinking 
that the reaction occasionally obtained is due either to phellonic 
acid or its salts or possibly in some cases to yet another suberin 
constituent. 
Similarly, van Wisselingh gave reasons for considering that in 
the case of the cuticle, where we have present a layer of cutin and 
beneath that the so-called “cutinized lamella,’’ where cutin-like 
substances are deposited in a cellulose layer, the upper layer of cutin 
is entirely devoid of a cellulose basis. 
Considerable emphasis is laid upon these conclusions, which seem 
to the writer to be well founded. They indicate a point of view which 
must be taken into account by plant pathologists when considering the 
entry of parasitic fungi through the uninjured plant surface or when 
discussing the possible effect of spray fluids on the plant they protect. 
