662 PROCEEDINGS OF THE 



biscuit tint. All are sprinkled with white crystalline particles. ' 

 The sporangium walls, usually very thin and fragile, are hard, 

 thick and chippy, and there is no distinguishable capillitium. 

 They are also only about half the ordinary diameter. The 

 spores themselves, generally bright brown and spinulose, are 

 smooth and almost colourless, but quite the usual size, if not 

 slightly larger, and in other respects appear perfectly normal. 

 Mr. Hilton had not yet attempted to cultivate these spores. 



The Hon. Secretary then read a paper on Hydrodictyon reti- 

 culatum, or utriculatum. Last September he found an immense 

 quantity of this alga in the lake in Kew Gardens. According 

 to Dr. Cooke the " water-net " is one of the earliest enumerated 

 freshwater algae in Britain. It is figured in PlukeneFs Alma 

 Geslum in 1691, and was again mentioned by Bobart in 1699. 

 Ray includes it in his " Synopsis " in 1724 as Conferva reticulata, 

 and says that it was found in ditches about Westminster and 

 Hounslow. Owing to various characteristics which are not 

 found in other algae, Hydrodictyon has been placed in a sub- 

 family by itself. It consists of a saccate net-like object varying 

 in size from almost microscopic up to a length of several inches. 

 The cells also vary in size when young from 8 /j. to 10 /x in diameter 

 and grow sometimes to a length of 1 cm. say, 2/5th-in. They 

 are approximately cylindrical in shape, and are arranged with 

 their ends in contact, usually three meeting at such an angle 

 as to form the typical hexagonal meshes. They have a some- 

 what thick wall, and inside a layer of protoplasm, in which the . 

 green chlorophyll is diffused, not collected into definite chloro- 

 plasts as usual in algae. The centre is filled with cell sap. The 

 protoplasm contains numerous and quite typical pyrenoids 

 each consisting of a central body with a layer of starch-grains 

 outside. These may be considered as food reserve. At the 

 commencement of reproduction they disappear, and are obviously 

 used up. There is also fine-grained starch in the protoplasm, 

 used for the purposes of life and growth. Many nuclei are pre- 

 sent in each cell. The net is born with a certain number of 

 cells, and always continues the same ; if, owing to injury, a part 

 is destroyed, it is not replaced. A small, complete net, con- 

 sisting, it may be, of some thousands of cells, is formed inside 

 each of the members of the original net. The mother cell-wall 

 gelatinises, and the young one is set free. What causes the ap- 



