recognize in plants any protective means against cold. The capacity of withstanding intense cold is a specific property of the protoplasm of certain plants, and is quite unassisted by protective means that are external.” It is a far cry from the high Alps to the seashore, but it will be of interest to examine next the lower limit of the range of the Seed Plants. While the upper limit varies much in different latitudes, according to the distribution of temperature, the lower is controlled by sea-level, which (for our purpose at least) is uniform over the whole globe. The level of the fresh waters, whose margin marks the limit of the bulk of the Seed Plants, is, on the other hand, various, lakes being situated at different heights above (and occasionally below) sea-level, while rivers slope across the lands down to the ocean. While the sea margin forms a very real barrier to the spread of Seed Plants, the lakes and rivers, on the other hand, yield many inhabitants, and we must examine the relations existing between the aquatic and the terrestrial species. As has been stated on a former page, the evidence points to life having originated in the water, at a period extremely remote. The most lowly as well as the most minute of all organisms are the bacteria, some of which are in size beyond the limit of the most powerful microscope to detect, their presence being known only by their chemical actions. The most primitive groups of bacteria, known as prototrophic, are able to live without light, deriving their nourishment by the breaking up of inorganic chemical compounds. It is difficult to conceive of any living organism more primitive than these, and quite possibly they recall that dim borderland where merely chemical structure and action mysteriously advanced into the cell structure and purposive chemical changes which we call life. From that lowly stage the evolution of plant life has been marked especially by three great forward bounds, of inestimable importance. The first of these was the “invention” of chlorophyll, which allowed plants to use for their life-processes the vast supply of energy furnished by the Sun. Sunlight then became essential to life, and the Algæ, the probable ancestors of all the higher plants, were developed, presumably through the peculiar _Cyanophyceæ_, or “Blue-green Algæ,” in which the chlorophyll is in a somewhat undifferentiated condition. Much later than this stage, yet far back in the history of evolution, occurred the second of the great forward steps. This was the desertion of the water for the land, which opened up for the plant world vast new fields and a great variety of new conditions. The final stage was reached by the abandonment of the aquatic mode of pollination by means of swimming spermatozoids, as still found in the Maidenhair Tree (_Ginkgo_), Cycads, Ferns, and groups lower in the scale, and the adoption instead of pollination through the medium of the air, “which” (to quote Mrs.