VIl] CYANOPHYCEAE. 131 



can hardly be taken seriously in such a case as this as an 

 argument in favour of the 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 un- 

 favourable 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^ 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 ex- 

 plosion. 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. 



In the petrified tissues of fossil plants there are occasionally 

 found small spherical vesicles, with delicate limiting membranes, 

 in the cavities of parenchymatous cells or in the elements of 

 vascular tissue. Some of these spherical inclusions have been 

 described as possibly simple forms of endophytic algae ^ such as 

 we are now familiar with in species of the Cyanophyceae and 

 other algae. So far, however, no recorded instance of such 

 fossil endophytic algae is entirely satisfactory. Some of the 

 A Treub (88). ' Williamson (88). 



9—2 



