232 



NATURE 



[May 22, iQi-j 



cavities in the embryo, but Hochstetter (1900) main- 

 tained that the early communication between the 

 cavities became closed completely, and that the canal 

 opening from one to the other in the adult is a new 

 formation. Mr. Goodrich shows, with the help of 

 excellent figures, that Balfour's original view is 

 essentially correct, and that Hochstetter was mistaken 

 in his interpretation. 



Among the Notes from the Laboratory of the Wis- 

 consin Geological and Natural History Survey is one 

 (No. II, issued December, 1918) by Mr. R. A. Mutt- 

 kowski on a qualitative and quantitative survey of 

 the fauna, with special reference to the insects, of 

 Lake Mendota, which has an area of about 15 square 

 miles and a maximum depth of 84 ft. That it forms 

 a rich collecting ground is evidenced by striking 

 records, e.g. a Myriophyllum plant with seven 

 branches, totalling a length of 4 metres, held more 

 than 15,000 specimens of Hydra fusca. Larvae of 

 Corethra punctipennis, which are abundant in the 

 lake, are found in daylight in the bottom mud, where 

 they chiefly hunt their food, but at night they come 

 to the surface. Catches made in the summer of 1916 

 by means of a dredge showed that the number of 

 larvae in a square metre of the bottom ranged from 

 2000 to 18,000. Despite the transparency of the larva 

 and pupa, these are eaten in large numbers by the 

 fish of the lake, perch gorged with these larvae being 

 frequently found. The larvae of the Ceratopogonine 

 genera Palpomyia and Probezzia, when grasped in 

 the water, straighten out and become rigid — one of 

 the few cases where aquatic insects feign death in 

 their normal environment. These larvae are slender 

 and elongate, and also resemble in their colour the 

 filamentous algae among which they live, but, never- 

 theless, they are frequent in the stomachs of the lake- 

 fish. The author cannot confirm Prof. Miall's state- 

 ment that those larvse of Chironomus which live at 

 the bottom and burrow in mud possess haemoglobin, 

 while those which live near the surface have colour- 

 less blood. He emphasises the absolute lack of any 

 correlation between colour and oxygen-supply. 



Mr. W. G. Craib (Notes from the Royal Botanic 

 Garden, Edinburgh, vol. xi., November, 1918) has 

 investigated the regional spread of moisture in 

 deciduous-leaved trees during the felling season — that 

 is, from late autumn until early spring. The species 

 selected for examination was the sycamore {Acer 

 pseudoplatanus), and the results, which are indicated 

 by graphs and coloured diagrams of cross-sections, 

 show that at the beginning of the season the centre 

 of the tree is very wet, and at the end of the season 

 there is a very wet region almost on the outside, while 

 the centre is very dry. Between these two extremes 

 are all the intermediate stages. The processes 

 during the season are interpreted as follows : As the 

 result of the water moving inwards from the outer 

 zones, beginning at the base of the trunk, there is 

 created an area of maximum moisture content, in any 

 given cross-section, at the centre of the trunk. This 

 inward current and the consequent plane of maxi- 

 mum moisture content at the centre gradually extend 

 upwards in the trunk to the topmost region; but 

 before this is reached and the centre of the trunk at 

 the top of the bole has become a region of maximum 

 moisture content, a radial movement has begun at 

 the bottom of the trunk. This radial movement also 

 progresses upwards, and by its means the region of 

 maximum moisture content passes almost to the out- 

 side of the trunk, leaving the centre the driest region. 

 The movements upwards and radially, both inwards 

 and outwards, are going on synchronously at different 

 levels in the trunk. The expressions _" the _ sap is 

 down " in autumn and " the sap is up " in spring are, 



NO. 2586, VOL. 103] 



therefore, meaningless; we should say rather "the 

 sap is in" (the centre) or "the sap is out" (near the 

 bark). These results in water-distribution are con- 

 firmed by experiments on other trees, and should do 

 much to remove the prejudice against summer fell- 

 ing. The new facts brought to light also raise points 

 of scientific interest as to the explanation of the 

 activities in the tree during the so-called dormant 

 period, or the reasons for the arrangement of the 

 various pits in the tissue-elements. 



The Sub-Committee of the Food Investigation 

 Board has issued an interim report on refrigerator- 

 cars, in which manv improvements are suggested 

 which could be carried out on existing cars, and 

 others which could be applied in designing new cars. 

 On the whole, the report reveals an unsatisfactory 

 state of affairs, with divided responsibility falling 

 partly upon the owners of the goods and partly upon 

 the railway companies. Tests were made on several 

 cars, both standing and running, showing that the 

 insulation is not so effective as is desirable; that the 

 deficiency in air-tightness is a serious matter; and 

 that the practice of icing the ice-tanks is altogether 

 inefficient. Another point worthy of note is the fact 

 that the cubic capacity of cars now in use is much 

 in excess of what tiiey can carry when they are 

 charged up to the safe load with frozen produce. This 

 is rather an unfortunate state of things. It is well 

 known that in order to obtain the best results in a 

 chamber containing frozen produce it is desirable that 

 it should be filled andi well stowed, whereas in some 

 cases the Committee found quite 35 per cent, of the 

 car-space was vacant. This defect might be remedied 

 by so designing the axles, etc., as to allow the present 

 cars to be loaded to their capacity. The Committee 

 would have pleasure in receiving from railwav com- 

 panies designs for refrigerator-cars embodying its 

 recommendations. 



A CORRESPONDENT forwards us a newspaper cutting 

 from South Africa directing attention to the possibili- 

 ties of the prickly pear (Opuntia, spp.) as a source 

 of industrial alcohol and other products. The plant in 

 question covers thousands of acres of good soil in 

 South Africa, and is a pest to farmers. To utilise it 

 profitably would be a notable achievement in turning 

 a waste product to account. Syrup can be obtained 

 from the plant, the seeds contain an extractable oil, 

 and an official report made some years ago is quoted 

 as indicating that alcohol might be produced from 

 the "tunas" or fruits at a relatively low cost. It may 

 be remarked that the question of producing alcohol 

 from the prickly pear has been carefully studied in 

 Australia ; the conclusion drawn, however, was un- 

 favourable. Analysis showed that the total sugar 

 content of the most common Australian species, 

 Opuntia inermis, was only o-6 per cent., and the 

 highest amount of sugar in any of the species 

 examined was but 2 per cent. Distillation experiments 

 yielded alcohol equivalent to only 0-5 per cent, of the 

 weight of the plant used, so that the manufacture 

 was considered unprofitable, and, indeed, scarcely 

 practicable. But the South African prickly pear is 

 said to be much richer in sugar than the Australian 

 product, and this, of course, may make all the differ- 

 ence between success and failure in utilising the plant. 



In the Transactions of the Institution of Engineers 

 and Shipbuilders in Scotland for December last there 

 is published an interesting paper by Mr. W. B. Hird 

 on "Electrical Ship Propulsion." The relative advan- 

 tages of the various electrical methods of driving the 

 propeller shaft are given, and also the results of trials 

 on ships with electrical gearing. To illustrate the 

 flexibility of the electric drive the author quotes the 



