Cytological Studies in the Protococcales. 
III. Cell Structure and Autospore Formation in Tetraedron 
minimum (A. Br.), Hansg. 
BY 
GILBERT MORGAN SMITH, 
University of Wisconsin , Madison , Wisconsin. 
With Plate XV. 
TTLE is known concerning the cytological structure of members of this 
J—/ genus. Several species are widely distributed in nature, but the alga 
never occurs in sufficient quantity to fix for cytological study. The obser¬ 
vations which I have made upon Teteaedron minimum are based upon material 
obtained by pure culture methods which have been described elsewhere (2). 
The cultures were grown in o -2 per cent. Knop’s solution and fixed in 
Flemming’s medium osmic-acetic-chromic acid mixture. The fixing solu¬ 
tion became diluted a fifth by the addition of the water containing the alga. 
The washing and dehydration were by means of osmosis through a celloidin 
film placed over the end of a phial as described in another connexion (3). The 
material was embedded in paraffin and cut on a microtome in sections 5 [x 
in thickness. Flemming’s triple stain gave the best differentiation of the 
pyrenoid and nucleus. 
The fact that autospores are formed in this genus has been noted by 
a number of investigators, and the citations compiled by Lagerheim (1), so 
that no further reference need be made to the subject. Good figures of 
autospore liberation from the old mother-cell wall are given by West (7). 
Lagerheim is the only one who has studied the nature of the cell contents 
and the manner of formation of the autospores. Fie states that there is 
a single nucleus and pyrenoid in T. minimum. In autospore formation he 
finds a transverse cleavage dividing the cell contents into two equal parts, 
and then successive cuttings dividing the cell into a definite number of 
autospores. Nothing is said concerning the behaviour of the nucleus and 
pyrenoid during this process, but his figures show a nucleus in each of the 
daughter-cells. 
The youngest cells I have observed always have a single nucleus with 
a pyrenoid in close association. The nucleus has a very conspicuous 
[Annals of Botany, Vol. XXXII. No. CXXVIII. October, 1918.] 
n h 
