90 Hardy, Alga^ of the Zoological Gardens, Melbourne, fvor^xxx 



of a few days' duration have temporary but not very marked 

 effects. Tlie colour is due to the great quantity of individuals 

 of a few species only. At times one species dominates, and 

 this, owing to causes not yet discerned, gives place to another 

 of allied genus, and this, perhaps, in turn yields to species of 

 different family, in one case the more advanced forms giving 

 place largely to a plant from which they may have been 

 phylogenetically derived. Towards the coldest part of the 

 year, there is a steady increase of the animal constituents of the 

 pool, such as rotifers, paramcecia, &c., and the plant organisms 

 decrease proportionately ; the winter season comprising late 

 May and June, July, and early August. 



In March, 1910, Botryococcus Braunii was visible at the 

 surface, and the following species were diffused in abundance : — 

 Scenedesmus quadricaiida, Merismopedia glauca, and a plant 

 somewhat resembling Kirchneriella Uinaris, and which was 

 dominant at that time. Considerable interest attaches to this 

 Last (Ankistrodesmus quaternus, W. and G. S. West), which hitherto 

 has been recorded only for the place where it was first collected 

 — viz., Burmah. The plant's typical habit is to appear as four 

 loosely aggregated cells, each crescentic, with obtusely-rounded 

 apices, and flattened somewhat, the four cells being opposed in 

 pairs in cruciform arrangement, with their concave edges 

 inwards. The local A. quaternus, which is embedded in a not 

 very distinctly defined gelatinous investment, and approxi- 

 mately of habit as above described, had not always the cells 

 regularly arranged. Though the convexities were usually 

 outwards, as in the type, the common axis of one pair of 

 opposing cells was frequently at right angles transversely to 

 that of the other pair, so that, when one opposing pair of cells 

 was viewed end foremost, the other pair appeared in side view. 

 If further investigation shows that this feature is as common 

 as inquiry up to date has shown it to be, varietal distinction 

 {A. quaternus, var. irregularis, proposed) may be necessarj^, 

 but I hesitate while examination of more material — not possible 

 at present — may prove this to be merely a phase in the progress 

 to maturity, and so the plant is referred to West and West's 

 species. An occasional isolated cell (seen as figured on 

 plate, fig. 2) having short spines, and thus resembhng 

 a single cell of Turner's Closteridium Bengalicum, gives me 

 doubt as to whether the last-named species exists in the 

 pool or that the cells of A. quaternus may occasionally bear 

 spines ; or, as a second alternative, that the connection 

 between the allied genera of this family may be closer than has 

 been hitherto regarded. Scenedesmus quadricauda ranked 

 second. There were comparatively few of Pediastrum duplex, 

 var. reticulatum, Ankistrodesmus falcatus, a species of Palmella, 

 and Navicula, sp. 



