October 7, 1922] 



NATURE 



495 



several occasions and is referred to in " Vegetable 

 Teratology," by the late Dr. Maxwell T. Masters. 

 While it is difficult to suggest a reason for the pheno- 

 menon with any degree of certainty, it is probable 

 that the condition may have been more prevalent 

 than usual this year owing to the prolonged drought 

 of 1921 and the early months of 1922, placing a check 

 upon normal development, followed by a rush of 

 vigorous growth brought about by the wet summer 

 months. A check to growth followed by a sudden 

 change to first-rate growing conditions often brings 

 about fasciation, and the median prolification of 

 flowers of Hemerocallis may be regarded in a rather 

 similar light to fasciation. 



Life -history of the Xeuropterous Insect 

 Ithone. — In the Bulletin of Entomological Research, 

 vol. xhi. pt. 2, August 1922, Dr. R. J. Tillyard gives 

 a verv detailed account of the biology of Ithone I 

 an Australian moth-lacewing. It appears that the 

 complete life-history occupies two years, and the 

 eggs are laid in soft or sandy ground, each being 

 rolled separately in the sand, which adheres to 

 its sticky surface, forming a protective covering. 

 The larva? are very different from those of other 

 Xeuroptera Plannipennia, being curved and more or 

 less scarabffiiform in their general features. There 

 appear to be at least five instars instead of the usual 

 three or four present in other members of the sub- 

 order. The cocoon is spun from the anal end of 

 the body, and the pupa is armed with large jaws 

 for cutting a way out for the emergence of the imago. 

 The larval food appears to be mainly scarabseid 

 grubs, and Dr. Tillyard is so impressed with the 

 value of Ithone in reducing the numbers of these 

 organisms, that he has decided to test its capabilities 

 as an aid to agriculture in New Zealand. Some 

 7000 fertile eggs of Ithone fusca have been introduced, 

 and it remains to be seen whether the larva? will 

 succeed in establishing themselves under the new- 

 conditions, and serve as a help towards controlling 

 the " grass-grubs." The latter are serious pests with 

 but few natural enemies in New Zealand. 



The Magnificent Spider (Dicroslichiis magnificus, 

 Rainbow). — In the Proceedings of the Royal Society 

 of Queensland (vol. xxxiii. 1921, pp. 91-98, pis. 7 and 8) 

 Mr. H. A. Longman ghes an interesting account of 

 this very large and handsome spider. It appears that 

 the creature constructs egg-cocoons of a more or less 

 elongate-fusiform shape, each being suspended by 

 a pedicel attached to a bush. Their total length 

 measures from three to four inches with a maximum 

 diameter of about one inch. The cocoon is double, 

 one cocoon lying within the other, and between them 

 is a loose packing of delicate silk. Within the inner 

 cocoon are the eggs, which number more than 600, 

 and, taking five cocoons as an average, each spider 

 lays about 3000 eggs. After hatching, the young 

 spiders climb up the surrounding leaves and spin fine 

 threads. On the latter they are floated, or ballooned, 

 through the air to start life on their own account. 

 The author gives a detailed account of how this re- 

 markable cocoon is spun by the parent, which, although 

 skilful in this art, had neither the capacity nor inclina- 

 tion to mend a rent in it when it was torn by a cricket- 

 like insect. The spider constructs no web for en- 

 snaring prey, but shortly after sunset it hangs sus- 

 pended from a horizontal line near its cocoons. From 

 this slender bridge it spins a short filament which hangs 

 downwards and terminates in a globule of viscid matter 

 a little larger than the head of an ordinary pin. The 

 filament is held out by one of the front legs, and, on 

 the approach of an insect, the spider whirls it with 



surprising speed ; this is undoubtedly the way in which 

 it secures its prey. Mr. Longman has repeatedly 

 found the spider sucking a common species of Noctuid 

 moth which it captures in this manner. 



Improved River Discharge Measurements. — In 

 the measurement of river discharge special difficulties 

 are encountered in the case of sluggish streams such 

 as the Blue Nile at Soba during low water. In a 

 report on " Investigations into the Improvement of 

 River Discharge Measurement," Pt. II. (Government 

 Press, Cairo), Mr. E. B. H. Wade gives the result of 

 his experiments with an improved current meter for 

 streams of this type. It is a helical current meter in 

 which the helix is driven not by the stream but by 

 an independent constant power. The effect of the 

 stream is merely to increase or diminish the rate of the 

 helix by an amount which serves as a measure of the 

 stream's velocitv. An instrument on these lines is 

 being constructed by Messrs. Kent and Co. The 

 distinctive feature of the model is that gear is dispensed 

 with, and instead of a weight with one or two kilo- 

 grammes falling about thirty centimetres, a weight of 

 25 to 50 grammes falls a distance of one metre. The 

 good results of this model are said to be due, in large 

 measure, to the directness of its action and the avoid- 

 ance of dissipation of energy in gear work. Experi- 

 ments made with instruments of this type gave 

 satisfactory results. The probable error for a single 

 determination was found to be +0-03 second, but Mr. 

 Wade believes that this will be reduced in the perfected 

 instrument. 



Turbulence on a Large Scale. — To sav that a 

 gas has viscosity, is a device to compensate in the 

 bulk for the motions which are ignored in detail. 

 Thus if the ignored motions are those within only 

 a cubic tenth of a millimetre the viscosity, for air, is 

 roughly 0-0002 cm. -1 grm. sec. -1 . If, however, we 

 ignore the gusts in a wind, then we must attribute 

 to the smoothed wind a much greater viscosity, 

 ranging, in the. same unit, from 1 to 100. In this 

 way the increase and veer of the mean wind in the 

 first kilometre above ground have been explained 

 by Akerblom, Taylor, Hesselberg, Sverdrup, Schmidt, 

 etc. Recently Albert Defant of Innsbruck has gone 

 a stage further by asking what the viscosity must 

 be if we ignore even the cyclones and anticyclones, 

 so that we are left with a smooth general circulation 

 of the atmosphere proceeding along the paths com- 

 monly shown in maps of the globe. A review of 

 Defant's first paper on this subj ect appeared in Nature 

 of April 15 last, p. 469. In a second paper, " Die 

 Bestimmung der Turbulenzgrossen der atmosphar- 

 ischen Zirkulation aussertropischer Breiten " (Wien, 

 Akad. Wiss., 1921), he re-examines, by other methods, 

 the viscosity to be attributed to this general cir- 

 culation, and finds, as before, values round about 

 io 8 cm. -1 grm. sec. -1 , that is to say, a billion times as 

 great as that arising by ignoring molecular agitation 

 only. This large value, 10 s , applies to friction 

 across vertical planes, but apparently the friction 

 across horizontal surfaces is an affair of gusts, 

 not of cyclones. When the viscosity is known the 

 conductivity for heat and for water vapour can 

 be found by the theories of G. I. Taylor and W. 

 Schmidt. The methods whereby Defant obtains 

 this viscosity include a computation of " eddy- 

 stresses " in accordance with Osborne Reynolds' 

 theory from the hourly values of the wind at various 

 heights. The direct eddy-stresses are in some cases 

 as big as 0-3 millibar. Defant also makes a deter- 

 mination by way of the scattering of air to north 

 and south of the mean-current after a passage of 

 3 days, using a formula due to L. F. Richardson. 



NO. 



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