588 JAMES BURTON ON HYDRODICTYON RETICVLATUM. 



at the end of June, and scarce a fragment to be seen in the 

 middle of July." Unfortunately there my page comes to an 

 abrupt end, but as there are several interesting points about 

 this alga, it may be worth while bringing them to the notice of 

 the Club. 



Owing to various characteristics which are not found in any 

 other alga, the genus Hydrodictyon has a sub-family to itself 

 and there is only one species. It consists of a saccate, net-like 

 object which ranges in size from very small, almost microscopic 

 dimensions up to a length of several inches, four, six and even 

 more. The cells of which the net is formed also vary very much 

 in size ; in the young ones they are quite minute, when first 

 recognisable from 8 to 10 ft in diameter only, but enlarge so 

 much in growth as sometimes to reach a length of 1 cm., say 

 two-fifths of an inch. The cells are approximately cylindrical 

 in shape and are arranged with their ends in contact, usually three 

 meeting at such an angle as to form typically hexagonal meshes, 

 but meshes with fewer or more boundary cells are- not uncommon. 

 They have a somewhat thick cell-wall, and inside a layer of 

 protoplasm, in which the green chlorophyll is diffused, not 

 collected into definite chloroplasts as is usual in algae. 



The centre is filled with cell-sap. There are very numerous 

 and quite typical pyrenoids in the protoplasm, each consisting 

 of a central body, with a layer of starch grains on the outside ; 

 these may be considered reserve food material. At the com- 

 mencement of reproduction they disappear, and are obviously 

 used up during the process. There is also a quantity of fine 

 starch grains in the protoplasm, these being used for the purposes 

 of life and growth. Many nuclei are present in each cell. 



The first point to notice is that the organism as a whole is 

 what is known as a coenobium ; it is, perhaps something more 

 than what is known as a colony, because the individual cells are 

 actually attached to one another, and form an association, 

 but certainly they are not greatly dependent on each other. 

 Each component cell is an individual, and carries on its living 

 functions independently ; for its own benefit solely it assimilates, 

 respires and reproduces, and were it separated from its fellows 

 would still be able to exist. We might then be inclined to 

 inquire what advantage the plant gains from the association 

 of so many units. One advantage is, that if the composing cells 



