April 2^, 1886] 



NA TURE 



607 



mean value of aio° finally adopted was 3'66, differing very 

 little from the above result. 



But if we examine the matter more closely we find that 

 the velocities for round 9, given by the two chronographs 

 at ^ were 9o7'4 and 88y2 m.s., showing a difference of 

 20'2 m.s., or 66'3 f s. ; and for round 10 there was a differ- 

 ence in the measured velocities at B of I9'4 m.s., or 

 63'6 f s. ; while at C there was only one velocity measured 

 for all four rounds, by one instrument ; so that the deter- 

 mination of the value of X in both the above cases was 

 made to depend upon one solitary velocity, measured by 

 an instrument manifestly unreliable. But at both A and 

 B the velocity adopted was an average of the results of 

 eight measured velocities. Consequently these velocities 

 at A and B may be expected to give a trustworthy value of 

 X over range A B, if the experiment be of any importance. 

 Substituting we find Xio* = 2'58, something very differ- 

 ent from its adopted value 3 '66. So that, according to 

 this group 3, the Newtonian law of resistance holds for 

 velocities between 900 and 438 m.s., and for velocities 

 between 853 and 438 m.s., but not for velocities between 

 900 and 853 m.s. ! Group 2 is still more inconsistent. 



Gen. Mayevski is also the author of an attempt to 

 express the laws of the resistance of the air to elongated 

 projectiles from extensive experiments said to have been 

 made at Meppen in 1881. The projectiles were more 

 pointed, and the standard density of the air adopted was 

 less than those used in England. Capt. Ingalls, having 

 reduced Gen. Mayevski's coefficients to English measures 

 for convenience of comparison, remarks, " It will be seen 

 that these coefficients are less than the corresponding 

 coefficients derived from Bashforth's values of A', given 

 above. This is undoubtedly due to the different forms 

 of projectiles used in the two series of experiments, and 

 particularly to the difference in the shapes of the heads" 

 (p. 21). My values of A' were derived from about 350 

 rounds, each of which in general furnished from 8 to 

 10 Lonsistcnt records, and gave numerous values of A' by 

 the help of a single chronograph. And the values of K 

 used in the above tables are the means of 40, 30, 20, 10, 

 &c., independent determinations of A' for each velocity. 

 Beyond a doubt they express accurately the average 

 results of the rounds fired. 



Although the shooting of recent guns is said to have 

 been improved, it is doubtful whether the coefficients of 

 resistance will require any sensible reduction on that 

 account for long ranges. For, as we have seen, 

 however steady may be the initial motion of an elong- 

 ated shot, the lateral action of the air must soon set 

 up a gyratory motion of the shot, and therefore the 

 axis of the shot must become oblique to the direc- 

 tion of motion. And we are told that a slight initial 

 unsteadiness of the shot becomes corrected, so that it 

 steadies down in its flight. This we might expect from 

 the nature of the action of the air on an elongated pro- 

 jectile rotating about its axis, which tends to place the axis 

 approximately in the direction of the motion of the shot. 

 But, if it should be found necessary to reduce the co- 

 efficient of resistance, this, as I have said, can be effected by 

 writing AV instead of A', where tr is less than i. But inas- 



much as we have to use — X Kt — -a X a, we must 



first calculate the value of tr, and then use the tabular 

 numbers in the usual manner. F. B.^SHFORTH 



PLANTS CONSIDERED IN RELA TION TO 

 THEIR ENVIRONMENT 



"T^ HAT great differences of constitution are to be found 

 •^ among plants is at once evident — differences affect- 

 ing internal structure, external form, and habit of life. 



Those of structure and form at first seem likely to be 

 correlated, and no doubt such relation to a large extent 

 does obtain, but still it is not at all exact, differences of form 

 occurring between plants whose intei'nal structure closely 

 agrees. The study of the environment of the particular 

 plant enables us to see that this must be taken into ac- 

 count in tracing the changes that have made it what it is, 

 each plant having a power of adaptation to circumstances 

 which determines the form which it assumes, which 

 modifies, though with extreme slowness, its internal struc- 

 ture, and which leads in course of time to the recognition 

 of new species. 



Looking at plants from this point of view, we notice at 

 once great differences between those which flourish in 

 water and those whose home is on land. These, again, 

 show diversities between those whose habit is terrestrial 

 and those which are epiphytic, while others are notice- 

 able whose habit of life is more or less completely para- 

 sitic, and whose constitution and structure are much 

 modified in consequence. 



A typical land plant will be seen to consist of a stem, 

 branching continually, bearing a variable but usually very 

 large number of leaves, and continuous below with a root 

 or system of roots embedded in the soil. The stem will 

 be characterised by a great development of wood, rigidity 

 being thus secured. The leaves will be noticeable espe- 

 cially for their great extent of surface in relation to their 

 bulk, and will show, generally on their under surfaces, 

 though very frequently on both, a large number of sto- 

 mata. The roots will be woody, like the stem, and 

 towards their ultimate terminations will be found to bear 

 a varying number of delicate root hairs, by means of 

 which they are enabled to discharge their special function 

 of absorption of water. 



This plan of construction is considerably deviated from 

 by plants whose habit is aquatic. The stiffness so essen- 

 tial to a land plant, which has to resist storms of wind, 

 is not at all essential to a water one, which has rather I o 

 adapt Itself to varying currents of water. JVIore fle.'ci- 

 bility, and that of a rather difterent kind, is needed by 

 the stem. We find, consequently, that the rigidity of an 

 aquatic plant is mainly arrived at by the development of 

 turgid parenchymatous tissue containing typically large 

 intercellular spaces, while the woody tissue largely dis- 

 appears. The intercellular spaces in most cases form a 

 very elaborate system, as may be seen on examining the 

 petioles of the large white water-lily {^Nyinphcea alba), 

 the stem of the common mare's-tail (Hippuris), or the 

 whole plant of difterent species of Fotamogeton. The 

 number of the fibro-vascular bundles is much less than 

 would be the case in the stem of a land plant of similar 

 dimensions, but the most noticeable difference is the rela- 

 latively much smaller amount of woody tissue in each 

 bundle. This difference of internal constitution may be 

 connected also with a functional ditt'erence associated with 

 the environment. The woody tissue of a plant is con- 

 cerned with the transmission of water upwards from the 

 roots to the leaves. In the case of an aquatic plant this 

 is not needed to anything like the extent to which it is in 

 an ordinary tree, and hence a further reason for the dis- 

 appearance of woody elements. Nor is it only the stem 

 which has been aftected by the habitat. The character 

 of the root will be found to vary. This is best seen 

 in noticing the efl'ect of allowing the root of an ordinary 

 land plant to come into contact with a quantity of water. 

 By its constitution it is fitted to absorb only the hygro- 

 scopic water surrounding particles of soil. The first effect 

 of the contact with excess of water is to cause the root 

 to perish ; but after a time new roots are developed which 

 can utilise the moisture they now are in contact with, and 

 which in turn are unable to avail themselves of the hygro- 

 scopic water which before was necessary. Both kinds of 

 roots may be seen sometimes on plants which have been 

 growing close to pipe-drains, some having penetrated the 



