M. Renault has recently described certain minute structures in a Palaeozoic coprolite to which he gives the name _Gloioconis Borneti_[204], and which he regards as a Permian gelatinous alga similar to the well-known recent genus _Glœocapsa_. The appearances revealed in a section of the coprolite are interpreted by this author as a collection of small colonies of a unicellular gelatinous alga in various stages of development. Renault’s figure shows a spherical group of faintly outlined and cloudy bodies, most of which include one or two small dark spots. The latter are regarded as the cells of the alga, and the surrounding cloudy substance is described as the gelatinous sheath. The absence of a nucleus in these extremely minute fossil cells (8–10 µ in diameter) is referred to as an argument in favour of referring the organism to the Cyanophyceae rather than to the Chlorophyceae. It is possible that the ill-defined structure described by Renault may be a petrified alga, but there is not sufficient evidence to warrant a decided opinion; the absence of nuclei can hardly be taken seriously in such a case as this as an argument in favour of the Cyanophyceae. [Sidenote: CYANOPHYCEAE.] Although our exact knowledge of fossil Cyanophyceae is extremely small, it is probable that such simple forms of plants existed in abundance during the past ages in the earth’s history. Several writers have expressed the opinion that the blue-green algae may be taken as the modern representatives of those earliest plants which first existed on an archaean land-surface. The living species possess the power of resisting unfavourable conditions in a marked degree, and are able to adapt themselves to very different surroundings. Their occurrence in hot springs proves them capable of living under conditions which are fatal to most plants, and suggests the possibility of their occurrence in the heated waters which probably constituted the medium in which vegetable life began. An interesting example of the growth of blue-green algae under unfavourable conditions was recorded in 1886 by Dr Treub[205] of the Buitenzorg Gardens, Java. In 1883 a considerable part of the island Krakatoa, situated in the Straits of Sunda, between Sumatra and Java, was entirely destroyed by a terrific volcanic explosion. What remained had been reduced to a lifeless mass of hot volcanic ashes. Three years later, Treub visited the island, and found that several plants had already established themselves on the volcanic rocks. Various ferns and flowering plants were recorded in Treub’s description of this newly established flora. It seemed that the barren rocky surface had been prepared for the more highly organised plants by the action of certain forms of Cyanophyceae, which were able to live under conditions which would be fatal to more complex types.