i 34 SCIENCE PROGRESS 



important than the conve} 7 ance of nutritive salts, also that the 

 living cells around the vessels form a glandular sheath for 

 secreting carbohydrates into the stream, the medullary rays 

 serving to store these and convey them to the sheaths. They 

 also give the results of cryoscopic and conductivity measure- 

 ments of sap pressed from the leaves, roots, etc., of trees after 

 treatment with liquid air, at intervals through the year, and find 

 that the osmotic^ pressure is mainly due to dissolved carbo- 

 hydrates, the concentration in deciduous leaves rising from bud- 

 opening to a midsummer maximum, while in evergreen leaves 

 the highest pressures occur in winter. Stiles (Ami. of Bot. 29) 

 claims to have disproved the view that the concentration of the 

 nutrient solution greatly influences the rate of growth of plants, 

 and finds that variation over a fairly wide range of concentration 

 has relatively little effect on the amount of dry matter produced 

 in rye and barley, also that plants grow quite healthily in a 

 culture of even lower concentration than that attributed to the 

 soil solution by Cameron. Osterhout has published two further 

 papers on protoplasmic permeability, using the method by which 

 he had previously shown that determinations of the electric 

 resistance of living tissues afford an accurate measure of per- 

 meability. He finds {Bot. Gaz. 59 ; Amer. Journ. of Bot. 2) that 

 permeability of protoplasm may be greatly increased or 

 diminished without injury, none being produced even with 

 rapid alternation of 20 per cent, above and 40 per cent, below 

 normal, also that while NaCl and other salts of monovalent 

 metals (and indeed all the monovalent kations except H) increase 

 permeability, all the bivalent kations investigated cause a marked 

 decrease. Ehlers (Amer. Journ. of Bot. 2) finds that evergreen 

 conifer leaves in winter maintain temperatures from 2 to io° C. 

 higher than the surrounding air, relates his observations to data 

 regarding photosynthesis at low temperatures, and suggests that 

 in them lies an explanation of the accumulation of winter-manu- 

 factured reserve food material by evergreen trees. Two 

 interesting papers on " symbiosis" may be mentioned here, both 

 in Ann. of Bot. 29. Rayner's valuable work on the mycorhiza of 

 Calluna (heather) has shown that we have here the first known 

 case of a green plant whose green as well as non-chlorophyllous 

 tissues harbour a symbiotic fungus; a similar distribution of 

 fungus mycelium, with ovarial infection of the seeds, occurs in 

 the darnel-grass, but this plant does not form mycorhiza nor has 



