yan..:,i, 18:9] 



NATURE 



But to return to the unknown drift-fruit. It is seldom 

 that specimens remain at Kew for a long period without 

 --omething occurring to call attention to them. It was so 

 in this instance. In November 1887, Mis. Hubbard sent 

 I'rof. Oliver a drift-fruit from the coast of Devonshire 

 \vhich was found to be exactly identical with the fruits 



oUected at Jamaica. The specimen had the same 

 water-worn appearance, and there was little doubt that it 

 had travelled across the Atlantic in the drift of the 

 (Calf stream. 



This fruit, a representation of which is given opposite, 

 possesses such distinctive characters that it can easily be 

 recognized. It is evidently a drupaceous fruit, but the 

 librous or fleshy outer layer (the sarcocarp) has either de- 



ayed or been worn away while drifting. What is now left 

 IS the woody indehiscent putamen or pericarp, externally 

 marked by amammillated surface corresponding,as shown 

 in sections, with numerous cavities or resin- cysts existing 

 in its walls. The fruit is normally five-celled, but two of 

 these are suppressed, and only three remain. The seeds, 

 as shown in Fig. 3, are solitary, and they possess abundant 

 <\lbumen. The presence of resin-cysts is a character of 

 ^ome value in seeking for the order or genus to which 

 such a fruit could belong. In the Kew Museums, there 

 ire some fruits collected by (J. Mann, on the Gaboon 

 River, West Africa, which afford a clue. These are the 

 fruits of Aubrya gabonensis, Baill, belonging to the natural 

 order Humiriacece (Oliver, " Flora Trop. Afr.," vol. i. p. 

 375). They are smaller than the Jamaica drift-fruit, and 

 ire covered with a brown, fibrous or leathery epicarp 

 3 millimetres in thickness. The bony endocarp is, how- 

 ever, similarly developed and plentifully furnished with 

 resin- cysts. The resemblance altogether is very close. 

 The natural order Hiimiriacccc is a very small one, and 

 ■consists of genera entirely confined to Brazil and Guiana, 

 with the exception of the single African genus already 

 inentioned. There can be little doubt that the drift-fruit 

 is derived from tropical America, and not from Africa. 

 The American genera of Humiriacece are Vantanea, 

 Humiria, and Sacoglottis (" Gen. Plant.," vol. i. p. 247). 

 It is not necessary to give all the details, but I may say 

 at once that Prof. Oliver is of opinion, and in this I agree, 

 that the drift-fruit will doubtless be found to belong to a 

 species of Humtria, and possibly to H. bals.iini/era, Benth. 

 (Hook., k'ew Journ., vol. v. (1853), p. 102). 



This species is said by Aublet (who figures the leaves 

 and (lowers only in " Plant. Guian.," p. 564, t. 225) to 

 grow in all the forests of P'rench Guiana, where it is 

 known, from the colour of the wood, as bois rouge. 

 Strange to say, the fruit of apparently so common a plant 

 IS unknown in European herbaria. Urban, who described 

 it, with a figure, in " F'lora Brasiliensis" (vol. xii. p. 439, 

 t. 92), had not seen a mature fruit. The specific name is 

 derived from the fact that the bark, when wounded, \ields 

 a reddish balsamic Juice, possessing an odour like that of 

 -torax, and which after a time becomes hard and brittle. 

 i I is then used as a perfume. An ointment is also prepared 

 lom it. 



For the present, therefore, we must leave the question 

 open as regards the exact determination of this drift-fruit. 

 1 here can be little doubt that it belongs to the genus 

 f/umiria, but. until we obtain fruits of H. babamifera we 

 Lie unable to say whether it is that species or not. 



D. Morris, 



P. S.— Since the above was in type, I have gathered 

 nformation which considerably increases the interest 

 onnected with this fruit. It is first figured and described 

 as a drift-fruit) by Clusius in bis " Exoticorum libri 

 !ecem,' lib. 2, cap. 19. This work bears the date of 

 1605. The description adds nothing as to the origin of 

 the fruit, except that it was received from Jacob Plateau. 

 The figure given by Clusius, with the description, is re- 

 produced by J. Bauhin, nearly eighty years afterwards, in 



'• Historia Plantarum" (1680), torn, i., lib. 3, cap. cxi., 

 Fig. I. There is another figure, still from a water-worn 

 and drifted specimen, given in " Petiveri Opera," tab. 

 Ixxi., Fig. 5 (1764), with the information that " it is a hard 

 oval fruit with seed-holes [resin-cysts] round its surface. 

 Cat. 605. Found on the shore of Jamaica." Finally, 

 Mr. E. G. Baker, F.L.S., to whom I am indebted for 

 the references to Bauhin and Petiver, has recognized 

 the fruit in the Sloane Collection at the British Museum 

 (Natural History), labelled "No. 1656." We are still, 

 however, without information as to the origin of the 

 fruit or the plant bearing it. D. M. 



HAZE. 



I HAVE for some time given in my lectures an. ex 

 planation of the common summer haze which 

 appears to me to be very probable. I do not know 

 whether it is new, but it has not been referred to in the 

 discussion raised by Prof. Tyndall's letter on Alpine 

 haze. Some time since I mentioned it to Prof. Lodge, 

 and at his suggestion I send it to you, though its extension 

 to other kinds of haze is somewhat speculative. 



It is that haze is often due to local convection cur- 

 rents in the air, which render it optically heterogeneous. 

 The light received from any object is, therefore, more 

 or less irregularly refracted, and, through the motion 

 of the currents, its path is continually varying. The out- 

 line of the object, instead of appearing fixed, has a tremu- 

 lous motion, and so becomes ill-defined. At the same 

 time, reflection occurs where there is refraction at the 

 surfaces of separation of heterogeneous portions. Much 

 of the light which, in a homogeneous medium, would 

 come straight from the object, is thus lost for direct 

 vision, and the contrast between neighbouring objects is 

 lessened. The reflected light is diffused as a general 

 glare. The combination of the quivering of outline, and 

 the loss of direct light, with the superposition of the 

 reflected light as a diffused glare, gives the appearance 

 we call haze. 



This explanation appears to me to accord well with 

 the obvious facts of summer haze— the haze which is seen 

 in the middle of a hot, cloudless, summer day. The 

 lower layers of air, being heated by contact with the 

 earth, rise in temperature till equilibrium is no longer 

 possible, and convection begins, streams of the heated 

 air rising, and streams of colder air falling to take its 

 place. Ihe variation of temperature and density gives 

 optical heterogeneity. The existence of these streams is 

 sometimes shown by the quivering of distant objects, 

 looked at through the air close to the ground, but a tele- 

 scope will often show the quivering of outline at higher 

 levels, and when quite invisible to the naked eye. Ac- 

 companying this refraction, refleciion must occur. We 

 have a direct proof of its occurrence in the fact that the 

 glare is greatest under the sun, where reflection occurs at 

 angles approaching grazing incidence, for which it is a 

 maximum ; while it is least opposite the sun, where re- 

 flection occurs at angles approaching normal incidence, 

 for which it is a minimum. The opening lines of the 

 "Excursion" perfectly describe the resulting appear- 

 ance :— 



" 'Twas summer, and the san had mounted high ; 

 Southward the landscape indistinctly glared 

 Through a pale steam ; but all the northern downs, 

 In clearest air ascending, showed far oflf 

 A surface dappled o'er with shadows flung 

 From brooding clouds." 



During the night the lower strata become colder than 

 the upper ones, and the atmosphere passes into a 

 state of stable equilibrium. We should therefore expect 

 that, if the foregoing explanation is true, there would be 



