18 



KNOWLEDGE. 



January, 1915. 



TRANSIT OF MERCURY AND OCCULTATION OF 

 PLEIADES.' — Fine weather favoured both these phenomena 

 at Greenwich. It was possible to deduce che times of con- 

 tact in the former witnin two or three seconds from the 

 combmed obseivations. Individual observers differed more, 

 some obviously timing apparent contact, others the snapping 

 or forming of the ligament or black drop. Numerous 

 measures of the diameter in various directions were made 

 during transit. The obseivers agreed in making the east 

 and west diameter about j" smaller than those inclined at 

 45° on either side of it. It is difficult to accept this a? 

 a physical realicy, but it is fupported by measures at 

 Several oiher obse ■vatories, and by M. Jonkheere's measures 

 at Lille in the transit of 1907. It will be necessary to wait 

 a long t;me for further observations (at least m tliis country), 

 as the transits of 1924 and 1927 will both end about an hour 

 after sunrise, and definition is bad at such small altitudes. 



More occupations were observed on December 1st than 

 in the whole year preceding. The Moon was so near full 

 that the stars disappeared verj' near the bright portion, 

 but in the case of the bright stars this was no hindrance 

 to accurate observation. Amateur observers wiU find 

 occultations very pleasing observations to make : they 

 take place with dramatic suddenness, and help one to realise 

 the rapid march of the Moon across the star- vault. Further, 

 if one can obtain accurate time, the observation and 

 publication of the time of the phenomenon are of real service 

 to science. 



BOTANY. 



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



CONSTITUTION OF CHLOROPHYLL.— Recent work 

 has shown that the familiar green pigment chlorophyll 

 is a very complex substance, and has given rise to a con- 

 siderable amount of controversy among plant physiologists 

 and biochemists. In a recent paper Stoklasa, in 

 collaboration with Sebar and Senft (Beih. hot. Cejitralbl., 

 Volume XXX), maintains his view that phosphorus is an 

 essential element in chlorophyll, and finds that it becomes 

 insoluble in alcohol or ether if dried leaves are used : this 

 he regards as explaining the statement of Willstatter and 

 others that phosphorus is not essential to chlorophyll. 

 The chemical constitution of chlorophydl extracts from 

 various plants is described ; phosphorus is present in pro- 

 portions of from 0-14 to 1-54 per cent, of the dry weight of 

 the chlorophyll extract. Stoklasa considers that chlorophjil 

 is made up of three different kinds of complexes ; (1) 

 Phaeophorb and metal groups soluble in alcohol and ether ; 

 (2) phaeophytin soluble in petrol ether; and (3) chloro- 

 lecithins, which are unions of either of these with phospho- 

 glycerides. Magnesium is one of the metals, and it 

 accompanies phosphorus. The colour-change of leaves in 

 autumn is regarded as a brealdng up of chlorophyll with 

 separation of phaeophytin and phosphatides, wliich are 

 brown in colour, and allow the yellow and red of xanthophyll 

 and carotin to appear ; the lecithins are not combined, but 

 are mixed with the chloroph^dl. The results of culture 

 experiments show that both phosphorus and magnesium 

 are necessary elements for the formation of chlorophyll, 

 as well as for the growth of plants generally, though only 

 in very small proportions. 



A NEW GRAFT HYBRID.— An account— the first, we 

 behave, that appeared in a British journal — of the work of 

 Baur and Winkler on graft hybrids and chimaeras, the 

 nature of which was discovered — or, perhaps more correctly, 

 rediscovered — and worked out in detail by these authors 

 appeared in " Knowledge " some time ago (Volume 

 XXXIV, page 136). Bois (Rev. Hort., 1914) has recently 

 given an account of a mixed hybrid, somewhat on the lines 

 of Cytisits adaml, which resulted from the grafting of a pear 

 upon a quince. The result of the grafting was the form- 

 ation below the graft junction of two opposite branches, 

 one of which showed quince characters, and the other those 

 of a form which the author names Pyrocydoiiia whikleri, 



differing markedly from both pear and quince. The 

 new form, moreover, could be propagated truly, which is 

 not the case with other mixed hybrids obtained in this 

 way. 



POLLINATION OF HERB ROBERT.— That even the 

 commonest of plants will repay careful investigation is 

 illustrated by the interesting study of the pollination in 

 Herb Robert (Geranium roberiianum) recently pubhshed by 

 Stager (Beih. hot. Centralbl., Volume XXX). His observ- 

 ations harmonise the contradictory statements concerning 

 the biology of tliis flower made by different writers ; for he 

 finds that it varies between a " fair-weather " type and 

 a " bad-weather " type. In fair weather the anthers shed 

 their pollen rapidly, and may finish doing so before the 

 stigmas are ready for receiving pollen, flowering taking only 

 half a day. In wet or cold weather, or in wet, cold places 

 even in fine weather, the stigmas develop more rapidly 

 than the anthers, and may take as long as three days to 

 mature. Among other interesting observations, the author 

 shows how colour, size, and the opening and closing of the 

 flower are aftected by light, though the chief factors con- 

 cerned are temperature and the humidity of the air ; for 

 instance, high temperature and dry air hasten the opening 

 of the anthers, wliile low temperature and damp air delay 

 their opening and favour the growth of the stigma. Hence, 

 according to external conditions, the flower may be either 

 protandrous (anthers ripening first) or protogynous (stigmas 

 ripening first), and in both cases self-pollination may 

 eventually take place. 



PROTHALLUS OF EQUISETUM.—TYve prothaUus 

 of Eqitisetiim has often been described, so far as the common 

 European and American species are concerned, as a creeping 

 body bearing irregular leaf-like lobes, some prothalli being 

 smaller and male, others larger and female. Kashyap 

 (Annals of Botany, Volume XXVIII) has now described 

 for the first time the prothaUus of an Asiatic species, 

 E. dehile, which proves to be of great interest. It is very 

 variable in its early stages, but frequently there is present 

 a " primary tubercle " similar to that found in the pro- 

 thaUus of some species of Lycopodium. The lobes are always 

 erect, and very close together, both in nature and in a 

 darkened room ; hence this position holds no relation to 

 the amount of light. One of the striking features of the 

 prothaUus is its radial structure. Hitherto a sharp dis- 

 tinction has been drawn between the prothaUus of Lyco- 

 podium and that of Equisetum, the former being radial and 

 the latter flattened (dorsiventral). Hitherto also the pro- 

 thalli of Equisetum have been generally described as 

 dioecious, the small prothalli being male (with antheridia) 

 and the larger ones female (with archegonia), though the 

 spores are all ahke in size ; but in E. dehile there are no male 

 prothalli, though sometimes a prothaUus produces no 

 antheridia, and is therefore female. The sexual organs 

 (antheridia and archegonia) of E. dehile, again, show resem- 

 blances to those of Lycopodium, and the author lays stress 

 upon the general affinity of this Equisetum prothaUus to 

 that of Lycopodium cernuum, remarking that there is no 

 more difference between the two than there is among the 

 different species of Lycopodium. This new Equisetum 

 prothaUus certainly disposes of the sharp distinction 

 hitherto drawn between the sexual generation in the two 

 great groups Equisetales and Lycopodiales, which, from 

 other facts, have long been regarded as having had a common 

 origin from the remarkable extinct group Sphenophyllales. 



CHEMISTRY. 



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



MEDIAEVAL SEALING WAX.— In the annual report 

 of the Government Chemist for 1913-1914, recently issued 

 as a ParUamentary Paper [Cd. 7562, pp. 1-25] an inter- 

 esting account is given of analyses of old wax impressions 



