260 



SCIENCE 



[N. 8. Vol. XXXIX. No. 



plants in half and full shade, but the per cent, of 



ash, figured on a dry matter basis, is less in these 



plants than in either of the other two sets of 



plants. 



Eelative Transpiration in Rain-forest and Desert 



Tlants: Porkest Shreve. 



Eelative transpiration is defined as the ratio of 

 the absolute transpiration of a unit area of leaf 

 snrfaee to the concurrent evaporation from a 

 unit area of water. Its values give an index of the 

 physiological controls of transpiration and of the 

 action of light upon it. Relative transpiration 

 and stomatal movement have been studied in sev- 

 eral Jamaican rain-forest plants, ivith the general 

 result that the two do not show a sufficiently 

 close correlation to warrant the view that either 

 is wholly controlled by the other. 



A comparison of the rates of relative transpira- 

 tion in rain-forest and desert plants shows them 

 to be of the same order of magnitude in the two 

 groups, as investigated under the conditions of 

 their native environments, in Jamaica and in Ari- 

 zona. Since the annual evaporation total in Ari- 

 zona is ten times that in Jamaica, it follows that 

 the absolute transpiration per unit area m plants 

 of the desert is approximately ten times as great 

 as it is in the rainforest. 

 Seasonal Variations of the Osmotic Pressure of 



Pool, Pond and Stream' Waters: Edgab N. 



Transeau. 



Freezing-point determinations of the osmotic 

 pressure of the natural waters of pools, ponds 

 and small streams in central Illinois, made at in- 

 tervals during the year 1913, have shown the fol- 

 lowing general results: 



1. The osmotic pressure, expressed in milli- 

 meters of mercury, varied from 59 to 407. 



2. The highest pressures were recorded during 

 early spring when the water levels were highest. 



3. The lowest records were made during the 

 middle of September when the levels for the year 

 were lowest. 



4. Contrary to the statements often made, when 

 the water level of ponds and pools lowers in late 

 spri'ng and summer, the osmotic pressure of the 

 water is not increased, but is often greatly di- 

 minished. 



5. When streams are reduced to pools, the water 

 may have a higher pressure; as the pools dry up 

 the pressure is diminished. 



6. There are sudden and considerable variations 

 in the pressure, sometimes coincident with weather 

 changes, development or decay of algas, etc., but 



sometimes without apparent connection with other 

 known factors. 



The year 1913 was an exceptionally favorable 

 one for testing the relation between lowering 

 water levels and concentration, as there were no 

 rains of consequence between the middle of April 

 and the middle of September. 

 Zoospore Formation in Characium acuminatum: 

 Gilbert Morgan Smith. 



The mature plant is multinucleate and contains 

 16, 32 or 64 nuclei at the time that zoospore for- 

 mation takes place. In the growth of the alga the 

 nuclear divisions are mitotic and all nuclei divide 

 simultaneously. There may be more than one 

 pyrenoid present and the shape of the pyrenoid is 

 quite irregular. Very thin starch plates are found 

 around the pyrenoid, while other plates of stroma 

 starch, probably derived from the pyrenoid, are 

 found scattered throughout the cytoplasm. 



The zoospores are formed by progressive cleav- 

 age. Cleavage takes place by a furrowing in of 

 the plasma membrane. The first cleavage furrows 

 are transverse and then longitudinal cleavage fur- 

 rows cut the protoplasm into multinucleate masses. 

 These multinucleate masses are then cut into 

 angular uninucleate protoplasts by further cleav- 

 age. There is no division of the pyrenoid, but it 

 remains unchanged till cleavage has been com- 

 pleted, when it disappears. The angular uninu- 

 cleate protoplasts then become ovoid and a pyrenoid 

 is formed de novo in each one. These are the zoo- 

 spores which are liberated by the rupture of the 

 old mother cell wall. 



A Preliminary Report on the Isolation and Identi- 

 fication of the Enzymes of Fucus vesiculosus : 

 B. M. DxiGGAK and A. E. Davis. 

 Peculiarities in the carbohydrate and nitrogen 

 metabolism of the Fucacese make desirable a de- 

 termination of the enzyme content of the growing 

 tissues. Employing a variety of methods, no evi- 

 dence has yet been foutnd to indicate the presence 

 of any of the commoner carbohydrases except 

 cellulase. The commoner esterases are likevrise ab- 

 sent, but amidases are well represented. Urea, 

 especially, is rapidly transformed and urease is 

 apparently widely distributed in the tissues. Oxi- 

 dases have not been detected by any of the usual 

 methods. 



Relation of Certain Grass-Green AlgcB to Ele- 

 mentary Nitrogen: Jacob E. Schramm. 

 The number of species of algE3 in which free 

 nitrogen fixation has been investigated under pure 

 cultural conditions is relatively small — represent- 



