38 Bristol . — On the Alga- Flora of some Desiccated 
bottom of the culture. Owing to the preliminary drying of the soil the 
cultures for some time contained only developmental stages of algae, and 
a considerable period elapsed before their identification could be accom- 
plished ; but it was easily seen that the green tufts consisted of filaments of 
moss protonema. At first only green algae and diatoms appeared to be 
growing in the cultures, forming a stratum on the surface of the liquid and 
on the sides of the culture-vessel, while the whole liquid assumed a light 
green colour owing to the presence of free floating unicells. Later, however, 
patches of blue-green algae began to appear on the surface of the soil and 
on the glass sides of the vessel below the surface of the water. 
Esmarch and Robbins in their investigations adopted rather different 
methods of culture from the above, but in neither case did the algae grow 
under quite natural conditions. Esmarch used Petri dishes about 2 cm. 
deep, in which he kept thoroughly moistened a layer of the soil to be 
examined ; on the surface of the soil he placed a piece of chemically pure 
filter-paper which was kept in close contact with the soil by constantly 
smoothing it out with a sterilized iron spatula. He found that the blue- 
green algae in the soil germinated and grew towards the light through the 
pores of the filler-paper and produced strata of various forms on the upper 
surface of the paper. He observed that green algae and moss protonema 
also grew occasionally, but very rarely in sufficient quantity to affect the 
culture to any extent. His result is thus quite different from that obtained 
in the present work, and unless the prolific growth of green algae in the 
cultures of English soils is to be regarded as a peculiar characteristic of the 
soils of this country, it appears rather as though the presence of the filter- 
paper in Esmarch’s cultures tended to suppress the growth of green algae or 
at any rate to prevent their penetration to the surface of the culture. Of 
diatoms Esmarch makes no mention, and it is probable that if they were 
present in the soils they never penetrated the filter-paper and so were com- 
pletely overlooked. 
Robbins for his cultures used half-litre flasks filled to their greatest 
diameter with washed and sterilized moist ground quartz, on the surface of 
which was distributed as evenly as possible io grm. of the soil to be 
examined suspended in 25 c.c. of distilled water. The flasks were tilted to 
one side so as to provide both a moist sand and a free water surface for the 
algae to grow on. In this way the algae were set to grow on a medium 
the physical qualities of which were quite different from those of the original 
soil in that all organic substance had been extracted from the quartz before 
use ; also the addition merely of distilled water without any dissolved 
mineral salts must have caused the algae to be subjected to a somewhat 
inadequate food supply, in view of the large quantity of insoluble sand 
present in proportion to the small amount of soluble salts in the inoculated 
soil. 
