920 REPORT—1899. 
high melting-point of the agar and the sliminess of some alge occasionally 
cause difficulties, 
The author has also succeeded in separating algze by the following methods :— 
2. Shake them up in sterilised nutritive mineral solutions, mix rapidly with 
silica jelly, also sterilised, and pour into glass dishes. With species of Oscdllaria 
and of Palmella the author has observed growth in hanging drops of this silica 
jelly medium under high powers, and has seen sufficient to make it hopeful that 
even Diatoms may be cultivated this way; and it is not impossible that some 
modification of the process could be utilised for the culture of marine alge, 
Another device is as follows :— 
3. Shake the algze up in the nutritive solution and rapidly mix with sterilised 
plaster of paris and pour into dishes. The fixed algze grow zm sztu in some cases, 
but others appear to be too sensitive for such treatment. 
Experiments have also been made as follows, with some promise of success :— 
4, The alge are shaken up in the culture medium, and a large quantity of 
lime-water quickly added. Then carbon dioxide gas is passed rapidly through, 
and the alg are thrown down with the precipitate of calcium carbonate; this is 
poured into dishes as if it were plaster of paris. Perhaps this method could be 
utilised in the study of calcareous alge, but with some forms it appears too 
drastic. It is possible baryta may succeed with some alge, but the trials have not 
yet been completed, and it seems to act as a poison to some. One drawback here is 
the difficulty of obviating the use of unsterilised materials. 
It is clear that if once we obtain a pure colony on a glass dish, a trace fished out 
with a needle may be used to start other cultures. Season, temperature, intensity _ 
of light, and other factors, are of importance in these matters. 
2. On the Growth of Oscillaria in Hanging Drops of Silica Jelly. 
By Professor MarsuaLty Warp, f£.2.S. 
Tn illustration of the applications of the methods for use in the culture of alge 
Professor Ward described the results of observations of the growth of Osczdlaria 
tenerrima in hanging drops of silica jelly. The growth of a single filament was 
followed for more than a week, and the curve showed that growth ceased during 
the hours of darkness, and was coincident with assimilation during the day. 
The author has also obtained light-figures by exposing plates of green alge, 
coyered with stencil letters, to various intensities of daylight, reflected from 
mirrors. When the incident light was not too strong a green letter on a colour- 
less ground was found, but with intense illumination the alge exposed on the 
letter was killed, while those in the covered area, iliuminated only by the diffuse 
light, were able to grow; the result was a colourless letter on a green ground. 
The division of the contents of certain green Protococcoidez into zoospores has 
also been seen in hanging drops of algar, &c. 
3. On the Life-history and Cytology of Halidrys siliquosa. 
By J, Liuoyp-Wit.iams. 
The chief points dealt with in the paper are the formation and liberation of 
the sexual cells, the striking phenomena accompanying the act of fertilisation, the 
segmentation of the spore together with the cytology of the various processes. 
is 
