August 3, 1905] 



NA TURE 



523 



A table given by Sir Philip Watts comparing- the 

 weights apportioned to the different elements of de- 

 sign in a battleship of 1805 and of a modern battle- 

 ship respective!)- is interesting. The old ship is one of 

 74 guns, and 20 per cent, of the total displacement was 

 awarded to general equipment as against 4 per cent, 

 for the 1905 battleship. Armament in - 1805 was 

 10 per cent, of the displacement; in the present day 

 it is 19 per cent. The propelling arrangements are 

 somewhat in the nature of a surprise, masts, sails, 

 and rigging absorbing 8-5 per cent., and steam 

 machinery only 10-5 per cent, of the displacement. 

 There is, however, to be added to the latter figure 

 55 per cent, for coal, but this is more than balanced 

 by the 6-5 per cent, of the weight apportioned (o 

 ballast for giving the stability needed under sail. 

 Armour is naturally the great point of difference, for 

 it takes up 26 per cent, of the displacement of a 

 modern battleship. As against this but 35 per cent, 

 of the total displacement is needed for the 

 construction of steel hulls, whilst the wooden hull 

 absorbed 55 per cent, of the total tonnage. It must 

 be remembered, however, that the construction of the 

 "wooden walls" was far more massive than was 

 needed for ordinarv purposes, and a good part of the 

 55 per cent, might be set down as wooden armour. 

 The remarkable thing is that iron plates were not 

 applied earlier, before the French constructors set us 

 the example ; or, rather, it would be remarkable were 

 the very conservative nature of the old admirals not 

 remembered. 



THE LIGHT-PERCEIVING ORGANS OF 



PLANTS.' 



'n^HE subject of this most suggestive book has 



-•• alreadv been dealt with by the author in a pre- 

 liminary wav.^ In its present form it has gained 

 greatly in force and interest, and whether or no we 

 are finally converted to Prof. Haberlandt's views there 

 can be no doubt that they are worthy of serious 

 attention. 



It is well known that the majority of leaves have 

 the power of placing themselves at right angles to 

 the direction of incident light, but the question of 

 how the light stimulates the leaf to perform the 

 curvatures and torsions which bring it into the " light 

 position " is a problem which hitherto has hardly 

 been attacked. 



, The first question to be solved is what part of the 

 leaf is sensitive to light. By covering the blade of 

 the leaf with black paper, &c., Haberlandt shows 

 that the principal and most delicate sensitiveness re- 

 sides in the blade, although a coarser and secondary 

 sensitiveness to the incident light is found in the 

 stalk. It results from this part of the inquiry that 

 the lamina of the leaf must contain the organs for 

 light-perception, if such organs exist. Anything 

 corresponding to a visual organ may be expected to be 

 on the surface, although in such a translucent organ 

 as a leaf this does not necessarily follow. It may, 

 however, be said that Haberlandt is amply justified 

 in looking for what he calls the ocelli of plants in 

 the epidermis covering the upper surface of the leaf. 

 We mav therefore narrow the problem thus. Imagine 

 a horizontal leaf illuminated bv light striking it 

 obliquely from above at 45° ; such a leaf is not in the 

 "light position," and will execute a curvature 

 through 45°, in fact until it receives light at right 



1 " Die Lichtsinnesorffane der Laubbl.^lter." By Dr. G. Haberlandt 

 o. 6. Professor der Botanik a. d. Universirat Graz. Pp. viii + 143 

 (Leipzitr- Engelmarn, 1905.) Price 6s. ret. 



- Berickte <i ticiitsch hot, Gtsellschn/t, Rd. xxii., 1904 (February), and 

 in an address given in 1Q04 before tbe Ge-ell-chaft deutscher Naturforscher 

 und Aezte, and published by Barth, of Leipzig. 



NO. 1866, VOL. 72] 



angles to its surface. Then curvature ceases and 

 the leaf remains in a state of equilibrium— satisfied, 

 as it were, with the " light position." The question 

 is how the leaf differentiates between oblique and 

 perpendicular illumination. Direct observation sug- 

 gests an answer. If the epidermis of such a leaf 

 as that of Begonia discolor be removed by a surface 

 section, and mounted upside down and illuminated 

 from below, then with a low power of the microscope 

 it can plainly be seen that there is a bright spot of 

 light on the basal (inner) walls of the epidermic cells. 

 It can further be seen that the relation of the spot of 

 light to the surrounding zone (which is more or less 

 dark) changes when the specimen is obliquely 

 illuminated. Thus in the case of the obliquely 

 illuminated leaf we should have to imagine that the 

 leaf is stimulated to curvature by the fact that the 

 spots of light are not central in the cells, and that 

 curvature ceases when the brightest illumination is 

 once more central. Thus the plasmic membrane of 

 the basal wall of each epidermic cell is supposed to 

 have a quasi-retinal function by which the leaf is 

 believed to orientate itself in regard to light. There 

 is here, as Haberlandt points out, a certain resem- 

 blance to the mechanism by which plants are by many 

 botanists believed to react to gravitation, namely, by 

 the pressure of solid bodies on different parts of the 

 cell walls, just as the statoliths (otoHths) of certain 

 animals, by pressure on different parts of the mem- 

 brane of the statocyst, enable them to orientate them- 

 selves in space. 



Haberlandt shows that the epidermic cell is well 

 fitted to concentrate light. It is ver>- commonly lens- 

 like in form, its outer wall being convex, its inner 

 wall either plane or curved. Haberlandt shows by 

 geometrical construction that, taking the refractive 

 index of the cell sap as equal to that of water, the 

 focus is usually at a point either within the cell or 

 below it in the other tissues. In either case a 

 central illuminated region and a surrounding dark 

 zone is produced on the basal cell wall. .\ further 

 development of this type is the papillose epi- 

 dermic cells which give the velvety appearance to 

 certain tropical leaves. This does not differ essentially 

 from the first described type, but it has, according 

 to the author, certain advantages which will be re- 

 ferred to later on. It must not be supposed that all 

 leaves have lens-shaped epidermic cells; some leaves, 

 known as aphotometrlc, are indifferent to the direc- 

 tion of incident light, and even in photometric leaves 

 Haberlandt shows that discrimination is possible 

 without the epidermis playing the part of a lens. 

 Where the outer wall of the epidermis is fiat, it often 

 occurs that the inner wall bulges into the subjacent 

 tissues or projects into them in the form of a trun- 

 cated pyramid. In this case, when the light strikes 

 the leaf" at right angles, the central part of the basal 

 wall, being more or less parallel to the surface, is 

 more strongly illuminated than its peripheral parts, 

 which are oblique. Thus without any lens-effect we 

 get stronger illumination in the central region of the 

 basal walls of the epidermis ; and _ this may con- 

 ceivably -serve as a means of orientation. 



The 'most conclusive proof of the author's theory is 

 given by the results of placing the experimental plants 

 under water. If he is right in claiming a lens- 

 function for the epidermic cells, it is clear that 

 immersion in a fluid which has approximately the 

 same refractive index as the cell sap must interfere 

 with the plant's power of light-perception; and this 

 is, in fact, the outcome of his experiments. 



His first experiments (p. 89) were made with the 

 hop (Humulus). Here, as in other cases, the stimulus 

 of light is perceived by the leaf, and less perfectly by 



