June, 1915. 



KNOWLEDGE. 



179 



and, if they left their parent planet in a state of close con- 

 centration, the expulsion need not last for more than a few 

 minutes. The close concentration is required equally on 

 the capture theorj-. For unless all the particles passed 

 at practically the same distance from the capturing planet, 

 their subsequent orbits would be very different. 



BOTANY. 



By Professor F. Cavers, D.Sc, F.L.S. 



TRANSPIRATION STUDIES WITH COBALT PAPER. 



— Among the many methods used for studying and giving 

 off of water vapour by plants one of the best known is that 

 in which thin blotting-paper is dipped in a solution of 

 a cobalt salt and then dried, becoming blue when dry, but 

 immediately changing to red when moistened. This method, 

 with modifications so as to standardise it, has been used in 

 making comparative tests of the transpiration of different 

 plants, the ratio of the time required for colour change of 

 the paper over a standard water surface to the corresponding 

 time required for the same change when the paper is applied 

 to the leaf of a plant giving the index of transpiring power 

 of the given leaf surface. An important paper, gi\'ing the 

 results of this method with a large number of plants, has 

 recently been published by Bakke {Journal of Ecology, 

 Volume II), who shows that the method is well suited to 

 the study of the daily march of transpiring power, and gives 

 valuable physiological and ecologica' results. This ratio 

 or index remains practically constant and low during the 

 night, but suddenly increases at about sunrise, attains 

 a maximum for the day some time before the occurrence 

 of the daUy maximum of temperature or of evaporation, 

 and then falls to the night value. Various plants, growing 

 under more or less arid soil and air conditions, gave differ- 

 ences in transpiring power which suggest that the same 

 species may possess quite different indices when grown 

 under moist conditions from those shown by individuals 

 grown under dry conditions. It appears that the magnitude 

 of the transpiring power is probably a physiological char- 

 acter that will be found to \ary for each species, within 

 certain limits, just as do the morphological characters 

 used in classification — leaf, size, shape, hairiness, and so on. 

 An important outcome of these studies is the conclusiou 

 that the method as employed by Bakke offers an apparently 

 adequate and simple means for classifying plant forms in 

 a scale of xerophytism or of mesophytism, according to the 

 transpiring power of the leaves. The term " mesophj^te 

 might be quantitatively defined as referring to plants with 

 average index of foliar transpiring power between -7 and I or 

 liigher ; while the term ' ' xerophy te ' ' may be considered as 

 connoting plants with an index below -3 ; plants with indices 

 between 03 and 07 would lie in an intermediate group. 

 The author's results with alfalfa and certain grasses show 

 that the agricultural problem of determining the relative 

 drought resistance of different crops or different varieties 

 should be approachable by means of this method, which 

 appears to be by far the most satisfactory yet suggested. 

 It is suggested also that foliar transpiring power may be 

 a characteristic of plants, the magnitude of which may 

 prove valuable in predicting the need of irrigation long before 

 the occurrence of any wilting. 



ORIGIN OF COAL.— This intcrestnig question is dealt 

 with from various points of view by \Vhitc and Thiessen 

 in a recent publication (Bulletin 38) of the United States 

 Bureau of Mines. The authors have studied coal and peat 

 geologically, microscopically, and chemically, and have 

 added much information regarding the structure, rate of 

 deposition, metamorphism, and so on, of coal. Some of their 

 general conclusions may be given. All coal was evidently 

 laid down in beds corresponding to the peat beds ol the 

 present day, and all kinds of plants, in whole or in part, 

 went into the deposit. The various materials entering into 

 plant structure differ widely in their resistance to the various 



agencies concerned in peat formation and subsequent coal 

 formation. At the death of the plants there begin, depending 

 on the conditions in the bog, partial decomposition, macer- 

 ation, eUmination, and chemical reduction, brought about 

 chiefly by organic agencies, chiefly fungi at first, and later 

 bacteria. Labile substances, hke proteins, are removed 

 first, and the more resistant next, lea\ing the most resistant 

 in the residue, which we call peat. These various processes, 

 conducted mainly by biochemical agencies, are taken up 

 and continued by dynamochemical agencies through various 

 later stages, resulting in the diSerent grades of coal, as 

 lignite, sub-bituminous, bituminous, cannel coal, and 

 anthracite. Hence coal is composed of the most resistant 

 components, of which resins, waxes, and higher fats, or the 

 derivatives of the compounds of which these are composed, 

 are the most important. These substances perform mainly 

 protective functions in plants, as in cuticles, spore coats, 

 bark, cork, and waxy coverings. The authors consider 

 that algae have not played any prominent part in coal- 

 formation, though this has been recently a somewhat con- 

 spicuous theory. 



BIOLOGY OF COWSLIP FLOWERS.— Dahlgren [Bot. 

 Notiser, 1914) has made a detailed study of the biology 

 of the flower in the Cowslip, with interesting results. As 

 to the early development of the flower, he confirms the \-iew 

 that the corolla arises as a series of five outgrowths from 

 the outer side of the same structures which produce the 

 stamens ; also that the wall of the ovary arises in the form 

 of a ring-hke upgrowth in the centre of which the placenta 

 grows up later, and quite independently. He watched the 

 development of the flowers through the winter : the flowers 

 are laid down in September ; the poUen mother-cells 

 are ready for di%ision and the o\ules recognisable by the 

 beginning of December ; by the end of February-, while 

 the soil was still frozen (the observations were made in 

 Northern Sweden), the pollen was nearly ripe, but the 

 ovules lagged behind. Some interesting data were obtained 

 regarding the results of legitimate and illegitimate fer- 

 tilisation. The author found that both kinds of pollen oc- 

 curred on the stigmas of both short-styled and long-styled 

 flowers ; that a good deal of illegitimate crossing takes place ; 

 and that, apart from the difference in weight of seeds 

 produced by the two methods pointed out by Dan\in, 

 there is, apparently, a constant difference between the 

 seeds formed by the two forms of flowers, those from the 

 long-styled flowers weighing on the average 0-001054 

 gramme, and those from short-styled flowers 0-000935 

 gramme. He also found that the seeds, when sown at the 

 end of July, and kept at a temperature of only 5° to 7° C, 

 germinated after four months ; hence they do not, as stated 

 by some wTiters, require a rest of two winters after being 

 formed. 



CHEMISTRY. 



By C. AiNSWORTH Mitchell, B.A. (Oxon), F.I.C. 



THE PHOSPHORESCENCE OF FLUOR-SPAR.— 

 Certain varieties of fluor-spar emit a pale green or violet 

 light when gently heated, while if the temperature be raised 

 the crystals throw off luminescent particles. Tlic cause 

 of this phosphorescence is attributed bv Dr. Formhals 

 (Cliem. Zeil.. 1914, XXXVllI, 1111) to the oxidation 

 of finely divided arsenic sulphide present in traces in these 

 varieties of fluor-spar. A specimen of felspar, which 

 showed no sign of phosphorescence when ignited, behaved 

 in an analogous manner after the addition of a trace of 

 arsenic sulphide. 



PHYSIOLOGICAL ACTION OF ALUMINIUM SALTS. 

 — The effect of small quantities of aluminium salts upon the 

 growth of plants has been investigated by Dr. Kratzmann 

 (Clieiii. Zeil . 1914. XXXVllI. 1040). The colouring matter 

 of red cabbage plants was changed to blue when the plants 

 were grown m a medium containing 01 per cent, of 



