150 



KNOWLEDGE. 



May, 1915. 



partially swollen state remains (or years in water restrained in 

 its swelling by the seed coat against which it exerts a pressure 

 of about one hundred atmospheres. When the seed-coat is 

 removed the embryo continues its swelling, which gradually 

 passes into growth enlargement. The pectic substances of 

 which the coat almost entirely consists are readily hydrolysed 

 by weak acids and bases, w Inch also change the water relations 

 oi these substances, as in the case of water-absorbing 

 colloids generally. Acids increase slightly the imbibitional 

 force of the embryo, while bases increase greatly the rate 

 ol elongation of the embryo. The effect of acids and bases 

 on the germination oi Alisma seeds is largely due to weaken- 

 ing of the seed-coat, so that the swelling embryo can break 

 away the coat-cap at the larger end of the seed. The 

 points of most obvious ecological importance are that the 

 seeds of Alisma, and probably those of water plants gener- 

 ally, are capable of lying in water for years in the imbibed 

 condition without losing their vitality, whereas those of 

 land plants can only withstand such storage for a short 

 time ; and that the embryo is capable, at the expense of 

 its stored food alone, of considerable growth in total absence 

 of oxygen, though it requires oxygen for development of 

 chlorophyll and a larger supply for branching and the 

 development of the primary root. 



THE FLOWER OF PARNASSIA.— The flower of 

 Parnassia (Grass of Parnassus) shows, as is well known. 

 a remarkable peculiarity in the form of a series of five 

 candelabra-like structures, one within each of the five 

 petals, alternating with the five stamens. These structures 

 are regarded as sterile stamens (staminodes) : each has 

 a solid honey-secreting base, and each of the branches 

 into which it divides above this ends in a yellow knob, 

 glistening in the light and looking like a drop of honey, 

 though it is a solid body. Flies, deceived by this appearance, 

 have been seen licking the knobs. The genus Parnassia 

 has hitherto been placed in the Saxifrage family, though 

 the resemblance between its staminodes and the stamen- 

 bundles in the flower of St. John's Wort (Hypericum) 

 has led some writers to regard Parnassia as related rather 

 to the Hypericum family. For instance, in some species 

 of Hypericum each anther contains a gland, and, if the 

 pollen-sacs of these anthers were to become abortive, we 

 should be left with a bundle of filaments, each ending in 

 a gland, exactly like the staminodes of Parnassia. Mrs. 

 Arber (Annals of Botany, Volume XXVII) has investigated 

 the structure of the Parnassia flower in detail and has, 

 found that each stamen contains, in addition to the usual 

 single vascular bundle present in stamen filaments, distinct 

 traces of a number of other bundles in a reduced or vestigial 

 condition ; hence the fertile stamens agree with the 

 staminodes in showing several bundles, though in a vestigial 

 condition. She also finds that the bundles destined for the 

 stamens arise at a lower level in the receptacle than those 

 which go into the staminodes, confirming the view that 

 the staminodes represent the inner whorl of the androecium. 

 It is suggested that the peculiarities in the anatomy of the 

 stamens of Parnassia indicate that each individual stamen 

 is reduced from an ancestral stamen-bundle like that of 

 Hypericum, and that the two genera are closely related ; 

 also that Parnassia should be placed in a separate family 

 instead of being classed in the Saxifragaceae. 



CHEMISTRY. 



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



COLOURS OF FLOWERS AS INDICATORS.— An 

 interesting study of the behaviour of the colouring matters 

 of flowers towards acids and alkalies is published by Mr. 

 H. W. Brubaker in the Journal American Chemical Society 

 (1914, XXXVI, 1925). The petals of most flowers, especially 

 those of blue, red, pink, and purple tints, are changed in 

 colour by alkalies, while acids restore the original colour 

 or produce some shade of red. The yellow pigments, how- 



ever, are unaffected by cither acids or alkalies, whereas 

 white flowers (white rose, pansy, clover, geranium) are 

 changed to yellow by alkalies, and back to white again 

 by acids. The reds and purples are turned to green or 

 greenish-blue by alkalies, while the original colour is 

 restored or intensified by acids. 



As a rule, these colouring matters are of an acid character, 

 and are less frequently neutral. They appear to be closely 

 related to one another, and it would seem that the different 

 variations in the colour of a certain flower or species of 

 flowers are the results of slight chemical changes in the 

 original pigment. 



So sensitive are some of these colouring matters to the 

 action of alkalies and acids that they can be used as chemical 

 indicators. For example, the red colouring matter of the 

 rugosa rose (Rosa rugosa) can be extracted with alcohol, 

 and the purified solution is turned green by alkalies, while 

 the red colour is restored by acids, and the liquid becomes 

 colourless at the point of neutrality. The indicator is 

 sensitive to carbonic acid, and changes colour in a solution 

 of sodium hydroxide, containing only one part in twenty- 

 five thousand. The colouring matters of the perennial 

 pea (Lathyrus latifolius), iris, and purple vetch behave 

 in an analogous manner, and appear to be either identical 

 with, or closely allied to, the pigment of the rugosa rose. 



CHARACTER OF CREOSOTE IN PRESERVED 

 TIMBER. — Most of the preservatives for timber are com- 

 posed of a basis of creosote, to which is added tar or coloured 

 pigments to meet the popular taste. These preparations 

 differ greatly in their preservative action, and considerable 

 light is thrown on the causes of these differences by an 

 investigation of Mr. G. Alleman (Proc. Amcr. Wood Pre- 

 servers' Assoc, 1914, page 88). 



The creosote oils extracted from well-preserved timber 

 that had been in use for several years were found to contain, 

 on the average, 32-9 per cent, of constituents boiling below 

 270° C. and 66-8 per cent, of constituents of high boiling- 

 point, ft is to a deficiency of the latter that the defects 

 of many modern creosote preservative must be attributed, 

 for the heavy constituents have much greater penetrative 

 and water-proofing capacity than the light oils. 



As the result of the experiments the conclusion is drawn 

 that for general purposes at least fifty per cent, of the oil 

 should distil above 315° C, and for treating pavement 

 blocks not less than sixty-five per cent. The penetrating 

 power of tar is small, even when injected at a high temper- 

 ature, and when a mixture of tar and creosote oil is emploved 

 separation of the components may be observed towards the 

 margins of close-grained rings in the wood. In the case of 

 light creosote oils loss is inevitable owing to volatilisation, 

 extraction of the oil by rain, and crystallisation within the 

 wood. The preservative effect of creosote appears to depend 

 partly upon antiseptic action and partly upon the interior 

 cell walls of the wood becoming coated with a stable film 

 of the oil, which excludes moisture. Light oils are rich 

 in antiseptic substances ; but, as these are soluble in water, 

 they are soon washed out of the wood by the rain. 



GEOGRAPHY. 



By A. Scott, M.A., B.Sc. 



INTERGLACIAL GORGES.— In those parts of the world 

 which show evidence of recent glaciation there is generally 

 considerable doubt as to the number of ice-invasions. 

 Such tests as the relative erosion of drift-materials of 

 different ages, or the amount of interglacial cutting by 

 streams whose profiles have been " de-graded " by ice- 

 action, are often difficult to apply. In the latter case, 

 the tributary streams may show several outlet gorges into 

 the main valley, which has passed through successive 

 stages of over-deepening. The number of gorges should 

 give the minimum number of interglacial periods, but not 

 the maximum, as there is nothing to hinder the re-excavation 

 of the old gorges. The width of the different gorges, con- 



