Nov. I, 1888] 



NATURE 



i^. 



THE COLOURING MATTER OF THE TESTA 

 OF THE SEED OF RAPE (BRASSICA NAPUS). 



7' HE testa of the seed of this species of Brassica is 

 dark brown in colour, so dark often as to appear 

 almost black. Being curious as to the chemical nature 

 ■f the colour in this outer seed skin, I made several very 

 ;npleexperiments(\vhich, however, have been thoroughly 

 iccessful) with a view to elucidate the matter. After 

 trying many solvents I was able to dissolve out the greater 

 part of the colouring material by the use of that very 

 common solvent, viz. a 25 per cent, solution of hvdrochloric 

 id. 



1 put two or three hundreds of rape-seeds into a large 

 ic.->t-tube (boiling-tube), covered them over completely 

 with tl:e dilute hydrochloric acid, and let the whole stand 

 for three days.^ 



.At the end of that time the solvent had acquired a very 

 distinct pale brownish-violet (inclining to magenta) colour. 

 When a little of this dilute hydrochloric acid extract 

 w as mixed with as much strong pure hydrochloric acid, 

 and gently heated, an intense yellow colour was developed, 

 pointing to the very probable presence in the solution of 

 iron in the ferric condition. 



When potassium ferrocyanide was added to another 

 portion, in a test-tube, of the original dilute HCl solution, 

 a pale greenish-blue colour, which gradually darkened, 

 was produced, and, after standing for about a day, the 

 characteristic Prussian-blue precipitate indicative of ferric 

 iron was observed to have settled to the bottom of the 

 tube. 



Potassium sulphocyanide confirmed the results obtained 

 above, by giving, when added to the original solution, a 

 well-marked blood-red coloration, showing the certain 

 presence of a ferric compound in the liquid tested. 



By these simple experiments I proved the presence of 

 iron. I now wished to ascertain the nature of the iron 

 compound in the testa which gave it. its characteristic 

 colour. I adopted the following simple method of 

 investigation : — 



I soaked for about a day a hundred or so of seeds. 

 Then I took off the s':ins, which the soaking had ren- 

 dered easily removable, placed them on a clean platinum 

 foil, and heated to and kept at a white heat till all the 

 water and organic matters were driven off, and nothing 

 but ash remained. This ash — which was very small in 

 quantity, of course — was reddish-brown in colour, and so 

 was tindoubtcdly, in large measure at least, ferric oxide. 

 When this red ash was treated with moderately strong 

 hydrochloric acid, the intense yellow colour due to the 



S ction of testa of rape-=:eed showing thick corky cell-walls iinpregnat;d 

 with hydraled (?) ferric oxide, (x i6o). 



production of ferric chloride was developed, and the 

 potassium fe-rocyanide and the sulphocyanide give the 

 characteristic tests recorded above. 



No doubt, then, was left in my mind by these experi- 

 ments that the iron existed in the state of ferric oxide 

 (most probably hydrated ferric oxide or limonite) in the 

 testa of the rape-seed. I was next anxious to know how 

 the ferric oxide was distributed in the corky tissue of the 

 testa. It soon occurred to me that this was also a very 



' I know now that it was not necessary to let the seeds remain in the acid 

 so lotig. By a little gentle and judicious heating for about twenty minutes 

 sufficient of thecoljuring substance woulJ be extracted to enable one to 

 determine its nature. 



simple matter to investigate. I embedded several testas 

 in paraffin, and by means of my microtome cut several 

 thin sections, mounted in water, and examined them with 

 a medium microscopic power. The cell-cavities were 

 entirely empty ; the thick corky walls were quite red. 

 There, then, in the walls, plainly enough, the ferric oxide 

 was seen to be distributed. 



How did the ferric oxide get into its place in these 

 walls ? This, I think, is the explanation. The iron was 

 taken in from the soil, by the root hairs of the plant which 

 produced the seeds, chiefly in the ferrous state, probably 

 as ferrous carbonate or chloride. It was conveyed in the 

 water stream through the parent plant to the seed, and 

 there deposited as an accessory substance in the cell-walls 

 of the testa amongst the corky matter while the process of 

 wall-thickening was going on. It was afterwards, or 

 during the process of deposition, oxidized and hydrated (i*), 

 and so the seed of Brassica Napiis acquired its charac- 

 teristic tough dark brown testa. 



Alexander Johnstone. 



Edinburgh University. 



THE TAIL-BRISTLES OF A WEST INDIAN 

 EARTHWORM. 



T HAVE recently received from Mr. Reginald Windle 

 ■*• a small collection of earthworms from Bermuda^ 

 among which is a new species showing a remarkable 

 peculiarity of structure which I have' not observed, or 

 seen recorded, in any other earthworm. 



The posterior extremity, for the length of about half an 

 inch (the worm measures about three inches), is furnished 

 with bristles, which, as in Utocliceta, are disposed in an 

 alternate fashion ; the eight bristles on each segment do 

 not correspond in position to those of the preceding or 

 succeeding segments, but are placed so as to correspond 

 to the intervals between them. 



In my specimen the bristles at the end of the body 

 were extremely conspicuous, and, when examined by a 

 lens, appeared to end in a thickened head ; the skin felt 

 sticky when touched by the finger. When a portion of 

 the body-wall was teased up in glycerine, and examined 

 with a microscope, the bristles showed the very remark- 

 able shape indicated in the accompanying woodcut (Fi/. 

 J, a). The bristle is very large — compared with those 

 upon the more anterior segments {b) and those of other 



Fig. x.—a, one of po^terio- s^tse ; b, «eta f j-n abjut mid Jle of body. Bath 

 drawn to scale with camera liicida. 



earthworms — and the free end is bent into a hook, the 

 point of which lies in a direction nearly parallel to that 

 of the shaft. The whole bristle is enormously thicker 

 than those which are found upon the anterior segments, 

 and of a deep yellow colour. At about the middle of the 

 shaft, where a slight swelling is commonly met with in 

 the bristlesof other earthworms, is a thickened rim which 

 suggests the attachment of powerful muscles. The hooked 

 end of the bristles accounts for the '* sticky '' feeling of 



