626 REPORT— 1889. 



apparatus with the tow-net attached is then thrown overboard, sunk hy a suitable 

 weight to the required depth, or is attaciied to the road of a trawl, and is towed 

 behind the boat. As it moves through the water the fan C revolves, and causes 

 the block D to ascend the screw. At first the tow-net is supported entirely by 

 the cords F F, which, being fastened through H to the two half-hoops Y, keep the 

 mouth of the tow-net closed. But when the block D arrives at the catches of the 

 tumbling-hooks /, it knocks them up, the tumbling-hooks fall down, freeing the 

 cords F F, and then the tow-net is pulled along by the cords Gr G attached to 

 the half-hoop X. The tow-net then opens, and remains open, whilst the block D 

 is travelling from /"/"to g g. On arriving at the catches of the tumbling-hooks gg, 

 the block in turn knocks these up and frees the cords G G. Now the whole 

 weight of the tow-net is thrown on the cords H H, carried by J J ; the mouth of 

 the tow-net therefore closes. 



In this form of apparatus the length of time for which the tow-net wiU remain 

 open depends upon the pitch of the blades of the fan, the thread of the screw, and 

 the length between gg and //. Thus if the pitch of the fan be 50", and the 

 threads in the screw 18 to the inch, the block will move one inch for every 10-12 

 fathoms traversed. If the ship moves at two knots per hour, and the distance 

 between gg and // is 14 inches, the tow-net will remain open for about b^ 

 minutes ; but by reducing the thread of the screw, and lengthening the distance 

 between g g and ff, this time could be very considerably increased. 



5. Third Report of the Gommittee for taking steps for the estahlishment of a 

 Botanical Station at Peradeniya, Ceylon. — See Reports, p. 114. 



6. On the Shape of the Oalc-leaf By Sir John Lubbock, Bart., F.B.8. 



We are so accustomed to the form of the oak-leaf that it does not strike us as 

 anything peculiar, and comparatively few perhaps have ever asked themselves why 

 it should be as it is. 



And yet it is peculiar, unlike that of any of our forest trees, and those of the 

 evergreen oaks so abundant in hotter countries. 



In botanical phraseology they are ' deciduous, oblong-oblanceolate, or oblong- 

 elliptical, sinuated, with blunt lobes extending not more than half-way down to 

 the mid-rib.' The sinus between the lobes is generally rounded off at the bottom. 



Again, though I have not found this mentioned in the botanical works which 

 I have consulted, they are rarely symmetrical, the lobes of the two sides not 

 corresponding. 



The three points, then, which give the oak-leaf its peculiar form are : — • 



1. The deep, rounded sinuses. 



2. The want of symmetry of the two sides. 



3. The oblong or oblanceolate outline. 



I do not know of any attempt to explain this peculiar form. As regards the 

 sinuses, Kerner suggests that they are intended to permit the passage of light to 

 the lower leaves. 



I would not deny that the space between the lobes may be of some advantage 

 in the manner suggested by Kerner, but I greatly doubt whether this is the main 

 or primary explanation. 



That which I would suggest is as follows. The leaves of the evergreen oaks 

 are entire, and small in comparison with those of the English oak. During the 

 winter and early spring they are protected by a series of brown scales, inside 

 which they lie, and with which they form the well-known buds which are so 

 familiar to us, and which are both small and short in proportion to the size of the 

 leaves themselves. 



In cooler and moister regions, on the contrary, there is, as we know, a tendency 

 for leaves to become larger and deciduous. I will not now enter into the reasons 

 for this, but the fact will not probably be denied. These influences do not, how- 



