Flood — Exudation of Water by Colocasia antiquorum. 507 



Duchartre found that it was nearly as pure as distilled water. Musset said it 

 contained traces of broken-down cells ; Haberlandt stated it contained a small 

 amount of solids; while Dixon (2) and Atkins (1) found that its freezing 

 point did not differ sensibly from that of distilled water, and its electrical 

 conductivity was less than that of tap-water. 



In the first place the structure of the leaf was examined. Externally 

 (PI. XLVIIL, fig. 1) it is peltate, with a simple, heart-shaped blade, often 

 60 ems. wide by 90 cms. long. The two lobes are directed upwards, and the 

 attenuated apex is directed downwards in the mature leaf. The petiole is very 

 long and thick, and its base forms a sheath round the younger petioles. It 

 joins the blade about three-fourths of the distance from tip to lobes, and at 

 the junction three large veins come off. These three give origin to smaller 

 veins, which ramify through the leaf, but both large and small eventually find 

 their way into a vein that runs parallel to and close to the leaf edge. This 

 vein joins the midrib just above the apex of the leaf. At the apex is a 

 pocket-like depression, about 3 mms. wide by 5 mms. long, in the floor of 

 which are from one to five circular pores, the larger with a diameter of about 

 O'l mm. It is from these that the water exudes. Below this depression the 

 apex is prolonged into a spur. 



The following features of the minute anatomy of the leaf may be noticed. 

 Under the epidermis of the petiole are bundles of fibrous strands, forming 

 sub-epidermal girders, while the vascular bundles are scattered through the 

 parenchyma, each with a large lacuna contiguous to it, and other lacunae 

 are distributed through the parenchyma. A transverse section of the blade 

 of the leaf shows that the epidermis is very papillate, and that the mesophyll 

 contains large spaces. Stomata are very numerous. The vein which is parallel 

 to the leaf edge is connected by small branches from its vascular bundle 

 with the vascular bundle associated with the innermost of three canals that 

 lie between it and the extreme edge (Plate XLVIIIa). A transverse section 

 of the edge of the leaf shows that these canals are lacunae formed in vascular 

 bundles (PI. XLVIIL, fig. 2). A few tracheids can be seen towards the under 

 surface of the leaf, and others are scattered round the margins of the lacunae. 

 These lacunae have apparently been formed by the walls of adjacent tracheids 

 ceasing to be in contact. PL XLVIIL, fig. 3, is a photograph of a transverse 

 section of a canal, and shows a split between two of the tracheids on the right, 

 and a few vessels isolated in the middle of the lacuna. The canals lead to 

 the apex of the leaf, and in it they become comparatively gigantic in size. A 

 transverse section of the apex (PL XLVIIL, fig. 4) shows that the pores in 

 the floor of the depression lead into intercellular spaces in the mesophyll. 

 These intercellular spaces are divided by lamellae and what might have been 



