May 15, 1879] 



NATURE 



55 



portant, therefore, to find out when the maximum average 

 density, or what is practically the same thing, the maximum 

 barometric weight of this stratum, occurs, and more especially 

 to see whether it coincides with the epoch of minimum tempera- 

 ture, which, as a rule, occurs in January throughout India. 

 The following table, in which I have calculated the mean 



Stations. 



Leh... 

 Lahore 



Elevation above 



sca-Icvcl in 



feet. 



... 11,538 

 732 



monthly barometric weight of such a stratum in different part 

 of the country, will show that the maximum invariably occurs in 

 January, that is to say, it coincides with the epoch of minimum 

 temperature. Two bars placed underneath a figure indicate 

 the maximum pressure or weight of the year ; one bar, the 

 secondary maximum at the hill-stations in the spring.^ 



Mean monthly barometric pressure in inches. 



October. 

 19-714 



29-144 



November. 



-707* 

 -262 



December. 

 •"332 



March. 



■656 



-107 28-962 



April. 

 -630 



Stratum between— thickness 10,806 weight 9*430 



Chakrata 

 Roorkee 



7,052 

 887 



23-332 

 28-965 



■555 



29-102 



-604 

 ■352 



•ISO 



•690 



•304 

 •108 



-666 



•313 

 -050 



•451 



•325 

 28965 



•332 



■309 

 ■853 



Stratum between — thickness 6, 165 weight 5-633 

 Darjeeling 6,912 23-436 



Goalpara 



386 



29-461 



-746 



:472 



•593 



•798 



•449 

 -641 



•804 



-382 

 -610 



•737 

 ■368 

 ■544 



-640 



•364 

 •459 



■544 

 •363 

 •383 



Stratum between — thickness 6,526 weight 6-025 -121 -192 



Ranikhet 6,069 24-108 -180 -158 



Lucknow ... .. .. 369 29-503 -651 "696 



•228 



•079 

 -641 



•176 



-070 

 -596 



-095 



■055 

 -481 



•070 

 •348 



Stratum between — thickness 5,700 weight 5*395 



Wellington 

 Madras 



6,200 



22 



24-217 

 29-847 



•471 



•245 

 •922 



•538 



•256 



•562 

 -208 

 ■944 



-526 



-226 

 •921 



•426 

 ■246 



•895 



•278 



•247 

 •843 



Stratum between — thickness 6,178 weight 5-630 -677 -709 -736 "695 -649 -596 



' To avoid repetition, I have merely given the decimals after the first column. In every instance of omission the last prefixed integer is to be supplied. 



Without going any deeper into the matter, it must, I think, be 

 generally admitted that the preceding facts not only dispose of 

 Sir. Broun's objection to the idea that pressure and temperature 

 are related, because the epoch of maximum atmospheric pressure 

 on the plains of India generally precedes that of minimum tempe- 

 rature, but also show how abortive any attempt to base induc- 

 tions regarding a secular variation in solar heat, upon the results 

 of comparing the annual range of monthly mean pressure, or even 

 the mean annual pressure, for a number of years in succession in 

 different parts of India, must necessarily prove, unless they be 

 duly taken into consideration. 

 ; With reference to;Mr. Broun's conclusions alone, the following 



modifications should be attached, according to the results of my 

 investigation. 



1. The annual oscillations of monthly mean pressure and 

 monthly mean temperature bear an exceedingly variable ratio to 

 one another in India, such variation being a function partly of 

 the altitude, and partly of the distance from the coast. 



2. Non-coincidence of the critical epochs of monthly mean 

 pressure and temperature, cannot be rigorously employed as an 

 argument against the hypothesis, hitherto generally accepted, of 

 a causal connection between them. 



E. Douglas Archibald 



Insect Galls Buds 

 Insect galls are held to be "excrescences"; a "diseased 

 c i.ndition of vegetable tissue " ; and they are supposed to result 

 from the "injection of a fluid," or from some " secretion." 

 The student may most easily begin an investigation of galls with 

 the dissection of those produced by the turnip weevil {Curculio 

 fleurosiigvia') on the bulb of the Swede. The roots of Swedish 

 turnips are frequently covered with hundreds of irregular 

 spherical warts, from '03 to -75 of an inch in diameter, growing 

 either singly or crowded together in clusters. These warts are 

 regarded by M. Woronin (Plasmodiophcra brassica, Prings- 

 heim's Jahrb. xi. B. p. 548) as resulting from the fungus which 

 he has discovered to be the cause of club-rooting in cruciferous 

 plants. 1 believe that on this point M. Woronin has been 

 misled. The true clubs produced by his fungus are entirely 

 distinct from these root-nodes. Under favourable conditions 

 the root-nodes have been found to give rise to tufts of leaves ; a 

 fact which I can confirm by many examples presently growing 

 in my po.ssession. Dissection of these nodes, on Swedes, shows 

 that they contain none of the plasma and spores which constitute 

 the bulk of the true clubs. They are, in fact, tuberculated buds 

 arising directly from medullary rays in the root to which they are 

 attached. These can be traced through the enveloping paren- 

 chyma into the nodes, where they are seen to give rise to masses 

 of contorted and branching leaves. The nodules within the bark 

 of the beech, hazel, and other trees, are of the same character as 

 those on the turnip. The medullary nexus of these nodules 

 sometimes comes straight from the centre of the tree into the 

 node, and sometimes runs along like a cord under, the outer 

 layers of the bark, entering the node by the end. 



Let a dissection now be made of one of the weevil galls on the 

 bulb of the turnip. The second or third shoe will show the outer 

 foliations, exactly similar to those of the root buds. When the 

 centre has been reached, where the maggot will be found, there 

 will also be found a vascular pencil running up from a medullary 

 ray in the bulb, and bearing on its top a bud of the same descrip- 

 tion as that produced by a ray running out from a root. The 

 insertion of the ovipositor brings a medullary ray into action, 

 producing a tuberculated bud, and it is only the bud which the 

 larva feeds upon. The growth of a bud is an intelligible cause 

 of the growth of a gall, but we can infer nothing from the injec- 

 tion of a fluid. 



All insect galls are in reality leaf -buds, or fruit-buds. They 

 are not mere amorphous excrescences. The vascular lines which 

 would form leaves can easily be followed up the structure of the 

 oak-leaf galls. And in cases where the egg has been deposited 

 in the tissue of a young branch the cap of the gall is sometimes 

 surmounted by a leaf two or three inches long. But in the large 

 blue Turkish galls many lacunae occur where the fleshified leaves 

 have not filled up the spaces between them. The morphology 

 of the hollow woody shell, and its inclosures of starch, &c., 

 found in the interior of these galls I hope to work out by and 

 by. It is a curious fact that various microscopic fungi are ma- 

 tured in the interior of imperforate galls. 



A. Stephen Wilson 



North Kinmundy, Aberdeen 



■ In selecting the particular station on the plains to be used in each case, 

 I have endeavoi red as far as possible to fulfil two requisites ; (i) prozunity 

 to the hill-sution, (2) low elevation above sea-level. 



