April. 1913. 



KNOWLEDGE 



145 



wind, and also to the pruning action of sharp salt or cold 

 winds, which shrivel up the buds on the windward side as soon 

 as they appear on the tree — this would account for the absence 

 of branches on this side of the tree, which is often observed. 



However, Jaccard (Journ. forest. Suisse, 1912) has called 

 this explanation in question, and has put forward a very 

 different one. He takes into account not only the general 

 form of the tree, but also the effect of growth in exposed 

 places upon the thickening of the trunk ; emphasizes the 

 fact that there is a close relationship between growth of 

 the leafy crown, the activity of the cambium or growing layer 

 between wood and bark, and the extension of the root system 

 in the soil ; and points out that variations in the rate of water 

 transport up the stem play an important part in the progress 

 and localisation of growth in thickness of the wood. He gives 

 the results of extensive comparisons of sections of the wood, 

 showing the anatomical correlation between roots, trunk, and 

 branches, in support of his contention that the modifications 

 in direction of growth, and in the secondary thickening of the 

 woody trunk and twigs, are due to various factors concerned 

 in the nutrition of the plant rather than to the mere mechanical 

 action of the wind, which he does not consider affords a com- 

 plete explanation of this familiar phenomenon. 



Jaccard's observations and interpretations are of great 

 interest, but further work on the subject appears to be 

 required before one can feel convinced that his main 

 conclusion is correct ; for it is somewhat difficult to see how 

 the characteristic T-shaped form of trees exposed to strong 

 winds can be fully explained without reference to the 

 mechanical action of the prevailing wind. 



THE GRAFT-HYBRID CYTISUS ADAML— The 

 remarkable experiments of Winkler and Baur on the pro- 

 duction of " graft-hybrids " and " chimaeras " were described 

 in these columns some time ago ("KNOWLEDGE," 1911, 

 page 186). At the meeting of the Royal Society on June 20th, 

 1912, Professor Keeble and Dr. E. F. Armstrong read a paper 

 on '■ The Oxydases of Cytisus Adami." The investigation 

 described in this paper was undertaken with a two-fold 

 object: (1) to test Baur's hypothesis that this graft-hybrid is 

 a periclinal chimaera composed of an epidermis derived from 

 Cytisus purpureus and a body derived from Cytisus 

 Laburnum, and (2) to ascertain whether migration of 

 oxydases (oxidising ferments) may occur in plants. The 

 results confirmed Baur's conclusions, and indicated that 

 oxydases may pass from one tissue to another. Tests 

 applied to the flowers of the three forms showed that 

 C. Adami and C. purpureus contain a direct epidermal 

 oxydase and that C. Laburnum does not; also that a direct 

 oxydase is contained in the veins of C. purpureus, while the 

 veins of C. Adami and C. Laburnum contain peroxydase and 

 not a direct oxydase. In other words, C. Adami is identical 

 with C. purpureus with respect to its epidermal oxydase, and 

 with C. Laburnum with respect to its bundle (vein) oxydase. 



The evidence pointing to oxydase migration is as follows : The 

 buff standards of C. Adami, like the yellow standards C. Labur- 

 num are marked by lines of chocolate colour, due to anthocyan 

 pigment contained in sub-epidermal cells. Sections across 

 these pigmented areas of C. Adami show that they coincide 

 with deeply pigmented epidermal cells. Over the other parts 

 of the standard the pigmentation of the epidermis is faint ; 

 over the sub-epidermal pigmented areas it is well-marked. 

 Inasmuch as the fainter pigmentation is due to inhibition of 

 pigment-formation it is concluded that the deeper pigment- 

 ation is to be attributed to the passage of oxydase from sub- 

 epidermal pigmented cells to contiguous epidermal cells. 



The failure of the buff flowers of C. Adami to develop their 

 purple pigment as fully as that pigment is developed in the 

 purple flowers becomes intelligible on the hypothesis of 

 oxydase-migration ; for, whereas the purple-flowered branches 

 contain a bundle oxydase which may reinforce that of the 

 epidermis in affecting pigment-formation, the vascular tissues 

 of C. Adami contain no direct oxydase and hence cannot aid 

 the epidermal cells in their work of pigment-production. 



In connection with this interesting " chimaera," mention may 

 be made of a paper by Janssonius and Moll (Rcc. trav. hot. 



Neerlandais, 1911, page. 333-368) on the minute structure of 

 the wood of Cytisus Adami and its components. These 

 writers find that, as might be expected, the wood of this form 

 closely resembles that of the laburnum and differs from that of 

 C. purpureus. The wood of C. Adami cannot be said to be 

 on the whole intermediate in structure between that of the 

 two " parents," but shows certain peculiarities which may be 

 due to the influence of C. purpureus. 



Buder (Ber. deutsch. bot. Ges., Band 28 ; Zeit. f. indukt. 

 Abst.-u. Verereb.-Lehre, Band 5) has made a very thorough 

 study of the minute structure of Cytisus Adami, and has 

 added various details to the descriptions of previous writers. 

 He also confirms the view, established by the work of 

 Macfarlane, Baur, and Winkler, that this form is a periclinal 

 chimaera. He finds that the protoplasm of the epidermal 

 cells is joined to that in the cells below by fine threads passing 

 through the cell-walls, just as is the case with the various 

 cells making up the living tissues of plants in general. The 

 nuclei of C. Laburnum are smaller than those of C. purpureus ; 

 those of the epidermis in C. Adami are of the purpureus 

 size, those of the underlying cells are of the Laburnum size. 

 In C. purpureus nearly all the cells contain tannin ; in 

 C. Adami it is present only in the epidermis. In C. purpureus 

 the cork-producing cambium arises in the sub-epidermal layer, 

 in C. Laburnum in the epidermis itself; in C. Adami the 

 cork may be formed from the hypodermis, or from the epidermis 

 or from both layers — all three cases may be seen in the same 

 twig. In such details as effect the epidermal layer of cells 

 (form of hairs, cuticle, stomata, and so on), C. Adami agrees 

 exactly with C. purpureus. A curious detail is the fact that 

 in C. Adami the nucellus of the ovule projects beyond the 

 micropyle ; this is easily explained as owing to the rapid 

 growth of the inner (Laburnum) tissue of the ovule as 

 compared with the outer (purpureus) integument. 



CHEMISTRY. 



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



. HYDRIDES OF BORON.— Many attempts have been 

 made to prepare definite hydrides of boron, but the instability 

 of these compounds has hitherto prevented their isolation in 

 a pure state. These difficulties have been overcome by 

 Messrs. Stock and Massenez (Ber. d. deut. Chem. Ges., 1912, 

 XLV, 3539), who have succeeded in preparing definite com- 

 pounds of hydrogen and boron by causing magnesium boride 

 to fall little by little into slightly heated dilute hydrochloric 

 acid. The gases evolved in the reaction were condensed in a 

 series of tubes chilled by means of liquid air, and the condensed 

 portions were then fractionated by replacing the liquid air, 

 first by a mixture of acetone and solid carbon dioxide ( — 82°C. 

 to -75 D C), then by liquid ammonia ( — 45°C. to — 35°C), and 

 finally by ice. 



By these means two hydrides of boron were isolated, with 

 compositions corresponding to the formulae B 4 Hioand B (i Hi*. 

 The first of these melted at about — 112°C, and easily decom- 

 posed into a series of other boron hydrides. In the gaseous 

 form it ignited spontaneously in the presence of air or oxygen, 

 and produced dangerous explosions in vessels with narrow 

 openings. 



The other hydride, B« H 12 , was a colourless liquid, which 

 had a repulsive odour, and, like its companion, took fire 

 spontaneously on contact with air. At the ordinary pressure 

 it boiled at about 100°C. It was readily decomposed by water, 

 and, when treated with alkali solutions, yielded hydrogen. A 

 trace of this hydride left in a vessel may give rise to a dangerous 

 explosion on admission of air, and it is recommended as a 

 precaution that the flasks should be rinsed with a solution of 

 sodium hydroxide before allowing any air to enter. 



THE BIRTH OF AN ATOM.— Two papers were recently 

 read before the Chemical Society, the importance of which to 

 physics and chemistry it is hardly possible to over-estimate. 

 At the time of writing, the official account has not been pub- 

 lished, but an excellent outline, taken from a report to The 



