334 MR. S. L. GHOSE ON A COLLECTION OF 
The mean temperature of the whole year is 54:8? F. During the months of 
December to March snow may fall, and may lie for several weeks on the 
ground. The period of heaviest rainfall is from June to September with an 
average of 52 inches, while the average for the whole year is about 70 inches. 
Blue-green algæ are met with at all times of the year in Lahore, but are 
most abundant after the rains, that is in the months of September, October, 
and November. Most of the Lahore Myxophyceæ are subaerial in habit, 
very few totally aquatic. This is due to the fact that there are no large 
permanent and stagnant sheets of water. The River Ravi, which flows ata 
distance of about three miles from the town, is too rapid to contain any free- 
floating blue-green alge in great abundance. After the rains or during 
floods, small ponds and pools are produced, which contain a few planktonic 
forms, but these disappear during the summer as the water slowly evaporates. 
After the rains a bluish-green slimy layer is generally formed on lawns 
and waste ground where water has stood for a short time. This is usually 
made up of species of Glaocapsa (rupestris, conglomerata, quaternata), 
Aphanocapsa (biformis), Nostoc (muscorum), Anabena (variabilis, gelatinicola, 
sp. n.), and Phormidium (autumnale). Tf the soil is clayey, like that near the 
banks of the river, Microcoleus vaginatus is often found growing on it. Bome- 
times beautiful circular patches, woolly or slimy in appearance, are seen 
scattered on the surface of lawns. These expand and finally coalesce to 
produce a brownish-green stratum, which for the most part consists of 
Campylonema lahorense, with which, however, species of Glaocapsa (rupestris, 
conglomerata), and Anabena (variabilis) may be intermingled. In the 
drains and constantly wet places species of Oscillatoria (tenuis) and Phorme- 
dium (autumnale) may frequently occur throughout the year. Sometimes, 
especially in the months of September and October, Symploca muralis and 
Cylindrospermum stagnale are met with adhering to the damp sides of the 
drains above the water-level. 
The aquatic blue-green alg® of Lahore are rarely free-floating. Clathro- 
eustis wruginosa, species of Arthrospira (platensis, spirulinoides, sp. n.), 
Lyngbya æstuarii, and Anabena spiroides var. contracta are the only forms 
found with this habit. Species of Merismopedia are occasionally met with, 
but are too infrequent for identification. Generally, the aquatic forms occur 
either on the surface of submerged plants or other objects, or adhering to the 
banks. Amongst the former are Chroococeus turgidus, species of Microcystis 
(litoralis, Donnelli), Chamesiphon filamentosa, sp. n., and Calothrix parietina; 
amongst the latter species of Oscillatoria (princeps var. pseudo-limosa var. 
nov., tenuis), Lyngbya (perelegans), Seytonema ( Fritschii, sp. n., crispum), and 
Rivularia (natans). 
Certain subaerial forms have adopted a peculiar mode of life. Tree-trunks 
of Acacia modesta are commonly seen to be covered with a bluish-green 
