276 



Fig. 20. 

 Transverse section of leaf of Kochia 

 scdi folia, only a few of the hairs are 



shown. 

 chlor., Chlorenchyma ; w.s.t., Water- 

 storage tissue ; m.r., Midrib ; s.v., 

 Secondary veins. xl5. 



O^DC 



Fig. 21. 



Absorbing hair of 



Kochia sedifolia. 



About X 300. 



There is a central main vascular strand and secondary strands around the 

 periphery of the water-storage tissue. No mechanical tissue, other than the 

 xyleni elements, is present. 



The chief point of interest in Kochia sedifolia, however, lies in the peculiar 

 type of water-absorbing hair which covers the epidermis. Each hair has a basal 

 cell with a large nucleus. This cell is larger than the neighbouring epidermal cells 

 and is partially buried in the assimilating tissue. The hair has a short stalk cell 

 which also appears to have living contents, and a very long terminal cell. The 

 latter cell has the spiral form shown in fig. 21. Near the base it usually makes 

 a few turns in the form of a compressed spiral, which becomes much looser 

 towards the terminal end. The cell has many small branches on its wall. These 

 usually project upwards toward the terminal end of the cell. The cell has very 

 thick cellulose walls and is non-cutinised. A narrow pore runs the length of the 

 cell. There are no living contents. The individual hairs are much intertwined, 

 so that the whole surface is covered with a thick felt of dead cells. The function 

 of these hairs is that of water absorption. The dead, air-containing cells probably 

 act as capillary tubes up which the water is drawn to the living basal absorbing 

 hair, and from which the water enters the leaf by osmosis. Such spiral hairs do 

 not appear to have been described in the Chenopodiaceae, although they have 

 been observed (without projections) in certain members of the Compositae — as, 

 for example, in Espeletia (Haberlandt, 1914). The peculiar small branches on 

 the terminal cell have been described in other members of the Chenopodiaceae, 

 Chenopodium muricafa and Enchylaena tomentosa (Monteil, loc. cit.J. 



DISCUSSION 



Having described the structural modifications found in the shoots, we are now 

 in ?. position to attempt an explanation of the types of transpiration curves in 

 the light of these modifications. Before so doing, attention must be drawn to 

 the calculations of Brown and Escombe (1900), who showed that the actual 

 maximum diffusion of water vapour from the leaf of H elianthus was only one- 

 sixth of the possible maximum diffusion calculated for the number and size 



