458 



SCIENCE. 



[N. S. Vol. XV. No. 377. 



curring in essentially the same manner as 

 in Hydrodictyon (Annals of Botany, Dec, 

 1901). In material killed in various kill- 

 ing fluids, sectioned with a microtome and 

 stained with the safranin gentian-violet 

 orange mixture, stages in the transforma- 

 tion of a portion of a pyrenoid into a 

 starch grain were observed. All the starch 

 ■grains arise in this manner. There is no 

 'distinction in origin between the so-called 

 pyrenoid starch and stroma starch. In 

 these cells starch cannot be said to be the 

 first visible product of photosynthesis, since 

 it is formed from a visible proteid body, 

 the pyrenoid. 



B. E. Livingston: ' Influence of the Os- 

 motic Pressure of the Surrounding Medium 

 upon the Growth and Production of Liv- 

 ing Organisms.' A change in the sur- 

 rounding solution may result in either a 

 physical or a chemical change in the solu- 

 tion contained within the organism. By 

 physical change is to be understood a mere 

 change in general concentration, brought 

 about by absorption or extraction of water. 

 A strong solution will extract water from 

 the organism, a weak one will allow it to 

 'be absorbed. By chemical change is meant 

 ■changes caused by absorption or extraction 

 of solute particles. Change in the water 

 eontent of the protoplasm may be directly 

 effective by causing a change in its phys- 

 ical properties. For instance, if water is 

 extracted, the viscosity of the protoplasm 

 must be increased. The same change in 

 water content may result in a change in 

 the chemical activity of the protoplasmic 

 solution, since chemical activity, in general, 

 ■depends upon the concentration of the so- 

 lution involved. How it comes about is 

 not knoAvn, but a review of the literature 

 of experiments upon animals and plants 

 : shows that growth is very much retarded 

 by an external solution which extracts 

 ■water. Especially is the elongation of cells 



retarded. The only experiment dealing 

 with the effect of external solutions upon 

 reproduction is that of the author upon 

 Stigeoclonium. Zoospores fail to be pro- 

 duced in strong solutions, but are produced 

 in large numbers in weak ones. 



H. G. TiMBERLAKE : ' GcU Division in 

 Biccia fluitans.' Attention was called to 

 the fact that the cells in the region of the 

 growing point afford excellent material for 

 the study of nuclear and cell division in 

 the liverworts. A distinct cell plate, whose 

 origin and development are the same as 

 that of the spermatophytes, can be made 

 out with very great certainty. 



HowAED S. Eeed : ' The Ecology of a 

 Glacial Lake.' The lake studied is the 

 remnant of a lake which came into ex- 

 istence at the close of the second glacial 

 period ; at that time its extent was consid- 

 erably greater than at present. As the 

 water level slowly fell, aquatic and semi- 

 aquatic species had the first opportunity to 

 get a foothold and become established upon 

 the land thus uncovered; as a result, the 

 flora of the region shows a scarcity of dis- 

 tinctly terrestrial plants. The plants at the 

 lake are grouped in five concentric zones 

 occupying all the lake bottom less than 

 twenty feet under water and the shores. 

 The zones which have been named from 

 their characteristic plants are as follows: 

 (1) Potamogeton, (2) Nuphar, (3) Carex 

 and 8phag7ium, (4) Salix and Populus, (5) 

 Grammece and Compositce. The position of 

 these zones is not permanent; they are 

 steadily encroaching upon the lake and 

 filling it ■with the soil they produce. The 

 most important agencies in causing the ad- 

 vance of the zones into the water are soil, 

 light and the moi-phology of the plants. 

 As the plants make the lake more and more 

 shallow they make it more unfit for them- 

 selves and fit for the succeeding zone. The 

 struggle in each zone is less successful on 



