160 Rudolf Beer. 
and some have suggested their close relationship to hemi-celluloses. 
Mangin disputes these assertions and believes that the pectic com¬ 
pounds stand apart from the carbohydrates. 
For many years a mucilaginous substance which Mangin has 
called callose was only known in its association with sieve-tubes. 
Mangin bas shown that it has a much wider distribution. He finds 
it in the pollen-grains of various Conifers, Cyperaceae and 
Juncaceae, as well as in the pollen-tubes of Plantago, Caltha , 
Narcissus , etc., in the walls of the pollen-mother-cells, in the 
cystoliths of the Urticales, and in the calcareous hairs and pericarps 
of several Borraginaceae. I have found it in the spore-mother-cell 
walls of certain Hepaticae e.g. (Anthoceros). Callose is only known 
to us by its micro-chemical reactions. Its true chemical nature is 
as yet quite obscure. Cuticularised and suberised walls have been 
very thoroughly studied by Gilson and Van Wisselingh. Both these 
authors believe that cellulose is entirely absent in suberised walls. 
Various acids have been obtained from the cork of different plants. 
These are phellonic acid , suberic acid and phloionic acid. Van 
Wisselingh regards cork-material or suberin as a fatty body which 
consists of glycerine esters and other compound esters as well as 
some further substance or substances which do not melt, are 
insoluble in chloroform, but are decomposed by K.O.H. solutions. 
Cuticularisation he regards as allied to but not identical with 
suberisatiou. It is due to the deposition of cut in. 
Phellonic acid is absent in cutin. The optical relations of cork 
indicate that its double refraction is due to the presence of 
regularly arranged particles of crystalline form which melt on 
heating and re-crystallise on cooling (Ambronn). Numerous 
attempts have been made to identify the substance or substances 
which cause the lignificatiou of the membrane. Tiemann- 
Haarmann concluded that coniferin formed a constituent of lignified 
membranes. Singer believed that the “lignin-reactions” depend upon 
the presence of vanillin as well as that of coniferin. Nickel and 
Seliwanow found that an aldehyde body occurred in wood. Czapek 
has recently pointed out that all the reactions which were used for 
the identification of the various bodies mentioned above are un¬ 
trustworthy. By boiling with zinc chloride Czapek has separated 
a substance which he names hadromal and which he believes is 
partly or entirely responsible for lignification. The concomitant 
of hadromal in the lignified wall is presumably cellulose and it is 
probable that the constituent of the lignified wall which produces 
