210 J. BURTON ON BOTRYDIUM GRANULATVM (l.) GREY. 



somewhat tender consistency it is difficult to extricate perfect 

 specimens. The upper part when young is filled with proto- 

 plasm and is bright green, later the centre becomes more 

 watery ; the green is then seen to be due to finely granular 

 chlorophyll. The roots are colourless and filled with watery 

 protoplasm. As to its classification, Prof. West, the most 

 recent authority on fresh-water algae, classes it with a group 

 called the Heterokontae, but with all deference T do not quite 

 see why. All the older books put it among the Siphoneae, 

 and it seems for several reasons to be very appropriately placed 

 there. One of the interesting facts connected with it is that, 

 although of such considerable size, it is unicellular. I suppose 

 that in thinking of a unicellular organism plant or animal 

 one usually considers it as something very small and micro- 

 scopic, but that is not necessarily the case. The Siphoneae are 

 a class grouped together because of the noticeable characteristic 

 that they are all unicellular, notwithstanding which, most of 

 them are of very considerable size. The best-known member 

 of the group is the exceedingly common Vaucheria. There are 

 many species, some terrestrial, constantly found on the damp 

 earth of flower-pots and on damp garden paths, and many 

 species occur constantly in ponds. In these plants, although 

 they reach a length of several inches, sometimes nearly a foot, 

 no dividing walls appear in the filaments, under normal vegeta- 

 tive conditions. Most of the family are marine, and one genus 

 occurring in the Mediterranean Caulerpa reaches a length 

 of several metres, and yet is not built up of individual cells. 

 The whole plant is a thallus, though in outward form appear- 

 ing to possess a stem, with roots and leaves. Similarly in the 

 little Botrydium we have a well-developed system of roots, 

 quite extensive in size (and, of course, acting physiologically 

 as such), and the upper swollen part, together of considerable 

 volume, and yet the whole is not divided or, rather, built up 

 of separate cells but has one undivided cavity throughout the 

 whole. 



Another point that strikes one is, where was the plant, or 

 in what form did it exist, while the mud on which it is found 

 was covered with water ? So far as I know the reservoir has not 

 been drained for many years ; and yet almost immediately the 

 water is drawn off, this organism appears in countless thousands 



