KNOWLEDGE. 



October, 1912. 



Figure 424. 



If r. II . Ill ', I\'^ denote their values in degrees, we may 

 instead of using the diagram find the distances from Jupiter by 

 the equations. 



Satellites are west of Jupiter when their angle is less than 

 500, or 180° after reducing to degrees. The original tables 

 contain a correction for light-time, but I have omitted this. 

 The quantities given here are for a mean light-time. The 

 tables also enable us to find the times of conjunction or 

 opposition of Jupiter. These phases occur when m is 500 and 

 respectively. For example to find when Jupiter is in 

 opposition in 1913. 



And since m increases thirty in twelve days (Table A4I, 

 we must go twelve days earlier to obtain the d.ilc of 

 opposition, which therefore occurs 1913. July 5th. 



isoi .\.\\-. 



By Proi-essor F. Cavers, D.Sc, F.L.S. 



SHORTENING OF WINTER- REST OF TREES.— 

 In recent years much attention has been paid to methods of 

 forcing based upon the awakening of activity in dormant 

 plants by means of warm water or anaesthetics. 



The etherisation of bulbous and other plants for the cut- 

 flower trade has, largely owing to the experiments of 



Johannsen, been successfully employed with lilac, mimosa 

 lily of the valley, and so on, and has proved remarkably 

 economical of time, space, and heat. The plants are exposed 

 for a day or two in a tight box to an atmosphere of ether 

 vapour, and after treatment are placed under conditions 

 favourable for growth. 



(iardeners have long known that placing the roots of plants 

 in warm water tends to start into more rapid and certain 

 growth dormant plants, especially when transplanting them. 

 Molisch has described interesting results based upon the 

 warm-bath method of forcing, which consists essentially in 

 immersing the plant or branch in water at a temperature of 

 30° to 35° C. for from nine to twelve hours, as a rule. When 

 potted plants are used, it is preferable to invert the pot and 

 immerse the stem only, since the roots are usually more 

 sensitive to injury. 



Jesenko (Bcr. dciitsch. hot. Ges., XXX, 1912) has recently 

 described a series of experiments with various trees and 

 shrubs, in which different substances were used in order to 

 shorten the normal resting-period. He obtained successful 

 results with immersion in alcohol and various acids, besides 

 water charged with carbon dioxide and plain water. He finds 

 that solutions of alcohol and acids gave better results in the 

 middle of the resting-period than towards its close, and that 

 immersion in a strong solution for a short period has the same 

 effect as immersion in a weak solution for a long period. It 

 is suggested that the action of the solutions used is not due 

 merely to a stimulus in the .strict sense of the word, but that 

 the solutions employed set up chemical processes in the plant 

 exposed to them. This view is supported by various observa- 

 tions; for instance, good results were obtained by injecting 

 the solutions into the twigs instead of immersing the latter in 

 the solutions. 



Burgerstein has published (Progressus rei hotanicac. IV) 

 a concise but useful sununary of the various new methods 

 used in forcing, .^fter describing the anaesthetic and warm- 

 hath methods, in connexion with the researches of Johannsen, 

 Molisch, and Howard, he deals briefly with the forcing effects 

 of frost and partial desiccation. He points out the .ipparently 

 paradoxical results of these modern experiments, which show 

 that the resting-period can be curtailed by cooling or by 

 warming ; by supplying the plant with warm water or by 

 depriving it of water by placing it in warm dry air : or by 

 treating it with narcotic vapours like ether or chloroform. He 

 concludes by stating that practically nothing can be said at 

 present in answer to the (juestions, how these various methods 

 of treatment act upon the plastic substances of the plant, why 

 it is easier to wake the plant up at an early stage in its 

 " sleep " than at a later stage, and so on. 



OFHIOGLOSSALES AND MA KATTIALES.— Professor 

 D. H. Campbell, of the Leland Stanford University, California, 

 has kindly sent the present writer a copy of his recent great 

 work on tlie lower ferns (" The Eusporangiatae " : Carnegie 

 Institution, Washington, 19111 — a fine quarto volume of 

 two hundred and twenty-four pages, with thirteen beautiful 

 plates and nearly two hundred text-figures. 



For over twenty years. Professor Campbell has studied the 

 Pteridophyta. or fern-alliance, and has published a large 

 number of memoirs on these plants, as well as some on the 

 liverworts, and his " Mosses and Ferns "' is a standard work 

 for the student of the Byrophyta and Pteridophyta. In this 

 sumptuous volume on the " Eusporangiatae." he brings 

 together a summary of the present state of knowledge con- 

 cerning the small but important families, Ophioglossace.ae 

 and Marattiaceac, which are placed at the base of the fern 

 series in the modern scheme of classification. 



Until comparatively recent times it was held that the ferns 

 in which the sporangium is developed from a single cell 

 (■' Leptosporangiatae") gave rise to those in which the 

 sporangium comes from a group of cells t" Eusporangiatae "). 

 on the ground that in this character at any rate the 

 former were simpler. It was held that the fertile spike 

 of Opliioglussum arose by fusion of numerous small 

 sporangia, and by further reduction and contraction the cone 



