English Soils : an Important Factor in Soil Biology . 65 
make it very probable that this alga is only a small form of C. marchicum , 
Lernm., a species not previously known to occur in this country. 
3 i. Plectonema Battersii , Gomont. 
The soil-form of this alga, which was observed in the cultures of no 
less than thirteen soil-samples, produced flat expanded strata of a dark 
brownish-green or black colour on the sides of the culture-vessels, consist- 
ing of numerous long filaments entwined together and repeatedly branched. 
The false branches were produced singly or in pairs, and were very slightly 
narrower than the main filaments and somewhat tapering towards the end ; 
the filaments were 2*5 to 3 /x broad and the cells considerably shorter than 
broad, with slight constrictions between them ; the end cell was rounded. 
The cell-contents were homogeneous and pale blue-green. 
22. Scytone7na javanicum , (Kuetz.) Bornet. 
The alga which has been identified under this name was found in 
two soils only, but in a third soil germinating spores of a similar form were 
found which never completely developed, and it is probable that they were 
early stages of growth of the same species. The filaments were agglutinated 
together and the sheaths were thin, becoming deep yellow ; they were 
usually about 12 /a in breadth. The vegetative cells were usually 9 to 10 [x 
broad and from 5 to 8 /x long. The heterocysts were brownish and hemi- 
spherical at the bases of the filaments, or compressed interstitially, but 
there was every indication in the cultures that the alga in question had not 
reached its mature form, and it is possible that at a later stage of develop- 
ment the heterocysts would obtain a more constant shape. The false 
branches were observed to grow singly and in pairs. This species has not 
previously been recorded from the British Islands. 
Bacillarieae. 
1. Navicula borealis , Ehr. (Text-fig. 8, 1 and 2). 
This species was observed in nine soils, and was one of the largest 
diatoms growing in the cultures. The form found was exactly typical of 
the species, but somewhat small, being only 40 to 44 /x long by 8-5 /x broad. 
There were 6 costae in 10 /x. The raphe was bent in the same direction on 
both sides of the median nodule and at the terminal nodules. 
2. Navicula Balfouriana , Grun. (Text-fig. 8, 3 - 5 ). 
The diatom that has been identified as this species agreed almost 
exactly with that figured under the same name in Schmidt’s ‘ Atlas der 
Diatomaceen-Kunde Heft 79 , Tafel 313 , Figs. 29-31. The costae were 
continuous along the whole length of the valve, and converged slightly 
towards the middle; there were usually 10 costae in 10 p, rarely 11 or 12, 
and the valve was oval, 18 to 24 /x in length by 5 to 6 p in breadth. The 
raphe was not bent in the same direction on both sides of the median 
F 
