* 0290 
In the aquatic tank near the Jodrell laboratory (briefly styled 
laboratory-tank in the subjoined list) a regular sequence of algal 
forms was observed, as will be seen from the following table :— 
E 8 
DTE ] : ?gd S T : E E 
sataj als ksa] a]? 
Simisdj«|mnie|s|-4]|- 
Characium Sieboldi .. «s - — "E — + 
Chlamydomonas pulviseulus .. | — -— — =- + + + + 
Chaetophora endiviaefolia "ope + +? — = = — A as 
Draparnaldia plumosa  .. AU Enid tes = = T T = T = 
Mesocarpus pleurocarpus .. -|- — + + — —- mes A 
Spirogyra crassa n ve a Eid m - + x n + > + E 
» condensata cae ee — — B T + — cu 
ns longata  .. ee T Puncta ES as Sm i + + + -— 
Closterium acerosum fe ee ee e + a Ae + + 
Sphaeroplea annulina a — — — + $ us e ET 
Cladophora fracta —|—|—-1|-1|- + $ X 4 
Ulothrix radicans -|-| -|— + sine na ow T ne 
Sciadium arbuscula -|/—-—-};—-J]—-|f- dcos desc aa 
Tetrasporalubriea .. nf A ~| — — -— — = 53 "m im 
The first Iuteresting form which appeared was Chaetophora 
endiviaefolia, which utterly sene after the & ak was cleaned 
out in April. A few weeks after this Draparnaldia plumosa and 
Sphaeroplea nnm the latter of which had been abundant at 
the same spot in former years, put in an BPDosraines, to be to a 
great extent superseded by two species of Spirogyra in the next 
month; finally, in July, Fetraspora lubrica appeared and has 
again vanished. 
Undoubtedly this great change in the vegetation of the tank 
in suecessive months is partly due to the ma ies Algae, which 
collects every few weeks, being removed, room being thus 
furnished for the abad of other species. "HG connection with 
this the sudden appearance of Chantransia pygmaea in the 
middle t tank of the trai house, a fortnight after it had been 
eaned out, may be mentioned. owever, other Algae show a 
priodi develbpment without any such agency coming into 
play. Thus Oscillaria nigra first appeared in the water-lily pond 
July ; in September it was far the most important constituent 
an qui 
cd in earlier parts of the pee is the most abundant Alga here. 
Much has already been written on the periodicity of certain 
plankton organisms (Clathrocystis, Anabaena flos aquae, &c.), 
but as far as I am aware too little attention in this respect has 
been paid d those inhabiting the deeper regions of the water. 
