254 
Holmes . — A Contribution to the Study of 
there occur at intervals radial rows of smaller water-conducting elements ; j 
most of these are perforated in their end walls, but the outermost are of the 
nature of tracheides, very similar in shape to the wood fibres. They have 
pits and spiral bands as in the vessels, and are well supplied with bordered 
pits on their tangential walls. At the limit of the year’s growth the last j 
tracheides frequently come into contact with the first vessels of the following 
year, and serve apparently to maintain a connexion with the latter, as stated 
by Strasburger ( 1 , p. 21 6). 
The mechanical function of the wood is served by the presence of 
a preponderating number of wood fibres, long pointed cells, empty, the 
Fig. 3. 
walls sparingly supplied with simple oblique pits. Surrounding each 
vessel is a zone of greater or less extent consisting of cells filled with starch 
grains, but otherwise closely resembling the empty fibres, as seen in both 
transverse and longitudinal section. They have simple oblique pits, chiefly 
on the radial walls, and their walls may be slightly thicker and more 
lignified than those of the neighbouring fibres. Strasburger ( 1 , p. 215) 
distinguishes these elements as dead and living wood fibres. At the end of 
each annual ring there is a layer, several cells deep, between the rays 
consisting almost entirely of living, starch-bearing fibres, and radial rows of 
vessels and tracheides. The cells decrease in size outwards in each annual 
ring, and become thicker walled and flattened towards this limit, which 
