448 Annals of the South African Museum. 



in several parts, but chiefly in the deep channel to the east of the 

 railway embankment. V. aureus predominated, but a fair amount 

 of the monoecious V. capensis was found. There were indications 

 that the latter species was in an early stage of development, e.g. the 

 presence of one or two " juveniles " from recently germinated oospores, 

 and the rarity of colonies with developing or mature oospores. 



Both asexual and sexual colonies are globose when young (Plate 

 XVI, fig. A), the polar axis only slightly longer than the equatorial, 

 but the sexual colonies often become considerably elongated during 

 the ripening of the oospores. The asexual colonies resemble those 

 from Rhodesia photographed by West in 1910 (Op. cit., pi. iii, figs. 1-7). 

 The average number of daughters is 8, but the number varies con- 

 siderably. There is also considerable variation in the size of the 

 protoplasts ; often these are similar in size to those of typical adult 

 colonies from the Cape Flats (5 to 7 p, in diameter), but other colonies 

 of approximately the same age occur in which the protoplasts are 

 considerably larger (8 to 10 /JL), giving the cell network a very much 

 coarser appearance. A similar variation was observed on the Cape 

 Flats, but there nearly always correlated with either the age of the 

 strain or the individual, or with external conditions. Here and on 

 the Linyanti, however, the various types occur side by side, and it 

 is impossible to say from the preserved material, collected over a 

 total period of only three weeks for the whole district, whether this 

 variation is characteristic of the form as a whole, or whether different 

 forms are actually present. 



Plate XVII, fig. A, shows a young sexual colony which was of the 

 large-celled type ; 5 or 6 mature sperm bundles and numerous young 

 oospheres are visible ; gaps in the cell network indicate positions of 

 sperm bundles which have escaped. Plate XVII, fig. B, shows in 

 more detail a small portion of the cell network with a very young 

 oogonium in the early stage of enlargement. This can be distinguished 

 in fig. A as a larger black cell a little below the centre to the left, next 

 to the oosphere directly above the large gap in the network seen near 

 the posterior pole of the colony. These photographs and Plate XVI, 

 figs. B-E, show what beautiful preservation may be obtained by 

 using Powers' Iodine method of fixation.* In Plate XVII, fig. B, the 

 star-shaped cells are practically undistorted ; the protoplasmic con- 

 nections are clear, but since they dip down below the point where 

 they unite with the protoplast they appear discontinuous. 



The sexual colonies are large in proportion to the asexual, but few 

 * See Chamberlain, Methods in Plant Histology, 4th eel., pp. 178-179. 



