98 



KNOWLEDGE. 



March, 1913. 



tree balloons have rendered to meteorology in giving records 

 of temperature, and so on, at heights inaccessible to man. 

 They have now been used to carry a Crova actinograph, and 

 so obtain a measure of solar radiation in a region where 

 atmospheric absorption is greatly diminished. He gives the 

 following determinations of the solar constant in calories per 

 square centimetre per minute at different heights : — 



1-5 calories at sea-level (winter). 



2-00 „ at 4,420 metres (Keeler, Mount Whitney). 



2-86 ,, in the isothermal layer at 13,700 metres. 



He concludes that the true value is 3-5 when there is no 

 atmospheric absorption. 



It is considered by some authorities that the solar constant 

 may itself vary by quite appreciable amounts, independently 

 of the action of our atmosphere. Professor Abbott suggested 

 simultaneous observations at distant stations to test this. If 

 they frequently varied together, the cause would probably be 

 in the sun itself, not in our atmosphere. I believe that such 

 a comparison is now being carried out between stations in 

 Africa and North America. 



BOTANY. 



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



STRENGTH OF TENDRILS.— It has long been known 

 that after a tendril has grasped a support it becomes much 

 stronger and produces increased hard tissue; but the details 

 have not hitherto been worked out satisfactorily. In an 

 interesting paper, Brush (Bot. Gaz., June, 1912) states that 

 passion-flower tendrils exposed to tension, and having also 

 formed contact with a support, had a much higher breaking 

 strength (over one thousand grammes) as compared with 

 tendrils in contact only (six hundred and fifty grammes) and 

 free tendrils (one hundred and ninety grammes). Tension 

 increases strength of tendrils sometimes by as much as fifty 

 per cent, in the middle third of its length. By radial pressure, 

 obtained by means of a mercury column in a rubber tube 

 enclosed by the tendril, an increased breaking strength was 

 obtained (nine hundred and ninety as compared with seven 

 hundred and thirty grammes). The breaking strength of the 

 tendrils was found to be increased by contact, pressure, and 

 tension. As regards the internal structure it was found that 

 the wood cells are increased both in number and thickness as 

 the result of contact, and that the walls of the pith cells are 

 thickened in consequence of tension. Just how contact, 

 tension, and pressure act as stimuli it is difficult to say, but it 

 is probably by bringing about increased hydrostatic pressure. 



LUMINOUS BACTERIA AND FUNGI.— Professor H. 

 Molisch has revised and enlarged his well-known work on 

 luminosity in plants (" Leuchtende Pflanzen " ; Gustav 

 Fischer, Jena, M. 7.50). Since the publication of the first 

 edition, eight years ago, various writers, notably Professor 

 Molisch himself, have contributed to the knowledge of 

 luminous phenomena in plants. Many of the cases of so-called 

 luminosity in plants are due merely to reflection of light which 

 is brought to a focus by lens-shaped cells, or are brought 

 about by iridescence or by the presence of fluorescent 

 substances ; but real phosphorescence — the emission of light 

 when the plant is placed in total darkness — is found in certain 

 bacteria and fungi. By isolating the bacteria which cause 

 the phosphorescence of meat and fish (Bacterium phos- 

 plioreum, Bacillus phosphoreus, and so on), and cultivating 

 them in nutrient jelly in tubes and flasks, Molisch obtained a 

 " bacterial lamp " with which he obtained some excellent 

 photographs, some of which are reproduced as illustrations in 

 his memoir. This " living lantern " can be used for a 

 photographic dark-room or as a night light, since the light is 

 strong enough to enable one to read a watch or to make out 

 large print quite readily. The light is steady and lasts for 

 several weeks, its intensity being about one candle-power per 

 thousand square yards of the gelatine plate culture. It 

 appears probable that the phosphorescence of these bacteria 

 is due to the production by the bacterial cells of a phosphorus- 



containing organic compound (" photogen ") of a proteid or 

 phosphatid nature, which in the presence of oxygen and water 

 undergoes slow oxidation — probably by means of an oxidising 

 ferment (oxidase). The light dies out if oxygen is withdrawn 

 from the culture or if the bacteria are dried, and reappears on 

 admitting oxygen and moistening the culture again. The 

 author discusses the cases of luminosity that have been 

 described in various flowering plants: for instance, on sultry 

 nights light is occasionally emitted by flowers, but this is 

 either an electrical phenomenon comparable with " St. Elmo's 

 fire " — a faint glow seen at the tips of masts and trees in 

 thundery weather, and due to the dissipation of atmospheric 

 electricity in the form of a brush discharge — or it is attribut- 

 able to the presence of small phosphorescent insects which had 

 been overlooked by earlier writers on " luminous flowers." 



HETEROSTYLED FLOWERS.— In a considerable 

 number of plants there occur long-styled and short-styled 

 flowers, as in the Primrose and other species of Primula, and 

 in some cases (as in the Purple Loosestrife) there may even 

 be three forms of flower with three lengths of stamen and 

 style. There is an interesting relation between the size of the 

 pollen grains and the length of the stigmatic hairs in these 

 flowers, the rule being that the longer the stamen the larger 

 are the pollen-grains, and the longer the style the longer are 

 the receptive hairs on its surface. Heterostyly raises several 

 interesting problems in heredity as well as in floral mechanism, 

 and Stevens (Bot. Gaz., April, 1912) has investigated the 

 development of the pollen and the other points in the life 

 history of two heterostyled plants — Buckwheat and Houstonia 

 coerulea. He found that in eighteen hours after " legitimate " 

 pollination (pollination of long-styled with short-styled) an 

 embryo began to develop, while in three days after 

 " illegitimate " pollination (pollination of short-styled with 

 short-styled or long-styled with long-styled) the pollen-tubes 

 had not reached the egg. Under natural conditions, there- 

 fore, there would be very little chance of illegitimate pollina- 

 tion resulting in fertilisation. The author gives various details 

 of the cytology and embryology in the two plants he 

 investigated. He found that in the development of the pollen- 

 grains the chromosomes in the reduction division are about 

 twice as large in the short-styled form, and that in the 

 long-styled form also the central chromosome is considerably 

 larger in one daughter-nucleus than its mate in the sister 

 nucleus. He compares this with the " accessory chromosome " 

 which is regarded as being the " sex determinant " in the 

 evelopment of the male germ-cells of certain insects. 



GERMINATION OF O RCH I DS— Some interesting 

 observations have recently been made on the fungi which are 

 associated with the roots of many orchids, forming a 

 " mycorhiza " or symbiotic (mutually beneficial partnership) 

 association between the fungus and the orchid. Burgeff and 

 Bernard have shewn that the seeds of various tropical orchids 

 will only germinate if the right micro-organisms are present. 

 By isolating and cultivating the spores or the " spawn " 

 (mycelium) of these fungi, pure cultures of the appropriate 

 mycelium can be made and used for mixing with the sphagnum 

 and fern compost in which the seeds are grown, the seed-pans 

 and the rain-water used for watering are sterilised, and suc- 

 cessful sowings are thus ensured. 



XEROPHILOUS ADAPTATIONS IN MOSSES.— Grebe 

 has published (Hedwigia, Band 52, 1912), a useful summary 

 of the adaptations of mosses for protection against drought. 

 He limits the use of the term " xerophyte " to those mosses 

 which grow in situations where they are exposed to fairly 

 prolonged periods of drought, are dependent upon atmos- 

 pheric moisture, and are not protected against drought by 

 other factors of the environment such as shade and damp 

 atmosphere. Warnstorf regards dependence on atmospheric 

 moisture, as opposed to that of the soil, as the chief 

 criterion of xerophily in mosses, but Grebe points out that 

 various mosses in shaded woods grow on tree trunks and yet 

 are not xerophilous, being protected against drought-periods 

 by their shaded and humid habitat. Many of the mosses of 



