ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
735 
Callose is amorphous, colourless, insoluble in water, alcohol, or 
Schweizer’s reagent even on addition of acids, readily soluble in a 
cold 5 per cent, solution of caustic soda or caustic potash, soluble in 
cold concentrated sulphuric acid, and in a cold solution of calcium 
chloride or tin chloride, insoluble in a cold solution of alkaline 
carbonates and ammonia, the latter giving it a gelatinous consistence. 
It is stained by anilin-blue and rosolic acid ; the iodine-reagents colour 
it yellow. It is not a product of the decomposition of cellulose or 
pectic substances ; its insolubility in ammonium-copper oxide, even 
after addition of acids, and its yellow colour with iodized phosphoric 
acid, distinguish it from the former ; its insolubility in a cold solution 
of ammonia and of alkaline carbonates, and its resistance to the 
staining reagents of pectic substances, from the latter. 
Callose is very widely distributed in the reproductive organs of 
Phanerogams and of Vascular Cryptogams ; the author found it in 
the pollen-grains of Coniferae, Cyperaceae, and Juncaceee, and in the 
plugs which interrupt the continuity of the pollen-tubes of Plantago , 
Caltlia and Narcissus. In the vegetative organs of Phanerogams it occurs 
in the bast-tissue ; elsewhere only occasionally, as accumulations in the 
interior of cells. In Fungi it plays a very important part, forming 
the membrane of the hyphae and of the reproductive organs in the 
Peronosporeae, Saprolegnieae, Basidiomycetes, Ascomycetes, and some 
Saccharomycetes. It is found also in the membrane of the spores and 
sporanges of the Mucorini, in the mycelial filaments of the Polyporeae, 
and elsewhere. In Lichens it exists in the membranes of the hyphae, 
but not in those of the gonids. Among Algae it is not nearly so 
widely distributed, but was detected in (Edogonium, Ascophyllum nodosum , 
and Laminaria digitata. 
(3D Structure of Tissues. 
Periderm.* — Sig. H. Ross adopts de Bary’s definition of this term, 
viz. all the tissues which spring from the generating zone known as the 
phellogen, and von Hohnel’s distinction of the three layers of which it 
is composed, — the outermost, phellema , composed of cork and phelloid ; 
the innermost, phelloderm ; while between them is the pliellogen. The 
principal protecting element is the phellema, composed of a larger or 
smaller number of layers of cells with walls entirely, or for the most 
part, suberized. The phellema, like the epiderm, has no intercellular 
spaces except the lenticels, which here and there break the periderm, as 
the stomates do the epiderm, in order to allow of the escape of gases. 
The segmentation of the phellogen takes place in a radial or tangential 
direction, in five different ways, which are described at length. 
The microchemical reactions for suberized cell-walls are described 
in detail, the best being concentrated sulphuric acid, which attacks all 
the cell-walls except those that are suberized, and chlor-zinc-iodide, by 
which the suberized and lignified walls are alike coloured yellow. In 
the greater number of cases the suberized wall of an isolated cell is 
composed of three lamellae, the median layer consisting of suberin, and 
the innermost of cellulose ; suberin consisting probably of a mixture 
of fatty substances. 
* Malpighia, iii. (1890) pp. 513-39; iv. (1890) pp. 83-123. 
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