_a._ CELL-SUBSTANCES. The cells of lichen hyphae contain protoplasm and nucleus with glucoses. It is doubtful if starch has been found in fungal hyphae; it is replaced, in some of the tissues at least, by glycogen, a carbohydrate (C₆H₁₀O₅) very close to, if not identical with, animal glycogen, a substance which is soluble in water and colours reddish-brown (wine-red) with iodine. Errera[768] first detected its presence in Ascomycetes where it is associated with the epiplasm of the cells, more especially of the asci, and he considered it to be physiologically homologous with starch. He included lichens, as Ascomycetes, in his survey of fungi and quotes, in support of his view that lichen hyphae also contain glycogen, a statement made by Schwendener[769] that “the contents of the ascogenous hyphae of _Coenogonium Linkii_ stain a deep-brown with iodine.” Errera also instances the red-brown reaction with iodine, described by de Bary[770], as characteristic of the large spores of _Ochrolechia_ (_Lecanora_) _pallescens_, while the germinating tubes of these spores become yellow with iodine like ordinary protoplasm. Glycogen has been, so far, found only in the cells of the reproductive system. Iodine was found by Gautier[771] in the gonidia of _Parmelia_ and _Peltigera_, _i.e._ both in bright-green and blue-green algae. The amount was scarcely calculable. Herissey[772] claims to have established the presence of emulsin in a large series of lichens belonging to such widely separated genera as _Cladonia_, _Cetraria_, _Evernia_, _Peltigera_, _Pertusaria_, _Parmelia_, _Ramalina_, and _Usnea_. It is a ferment which acts upon amygdalin, though its presence has been proved in plants such as lichens where no amygdalin has been found[773]. Diastase was demonstrated in the cells of _Roccella tinctoria_, _R. Montagnei_ and of _Dendrographa leucophaea_ by Ronceray[774] who states that, in conjunction with air and ammonia, it forms orchil, the well-known colouring substance of these lichens. Diastatic ferments have also been determined[775] in _Usnea florida_, _Physcia parietina_, _Parmelia perlata_ and _Peltigera canina_. _b._ CALCIUM OXALATE. Oxalic acid (C₂H₂O₄) is an oxidation product of alcohol and of most carbohydrates and in combination is a frequent constituent of plant cells. Knop[776] held that it was formed in lichens by the reduction and splitting of lichen acids, though, as Zopf[777] has pointed out, these are generally insoluble. Hamlet and Plowright[778] demonstrated the presence of free oxalic acid in many families of fungi including _Pezizae_ and _Sphaeriae_. The acid combines with calcium to form the oxalate (CaC₂0₄), which in the crystalline form is very common in lichens. In the higher plants the crystals are formed within the cell, but in lichens they are always deposited on the outer surface of the hyphal membranes, mainly of the medulla and the cortex.