THE FUNCTIONS OF THE WOOD 201 



FUNCTION OF THE LIVING ELEMENTS OF THE WOOD. 

 Examination of sections for the estimation of the starch 

 content of the wood cannot fail to force on one the remark- 

 ably regular and close connection existing between the 

 starch-containing elements and the vessels. Further, 

 when we take into account that the transference of carbo- 

 hydrates can no longer be regarded as an occasional and 

 accessory function of the vessels, but is certainly a con- 

 tinual and principal function, the starch layer round each 

 of them becomes evidently a glandular sheath to the 

 vessel for the secretion into it of the sugars to be trans- 

 mitted upwards. The location of starch in the elements 

 on the borders of the year-rings is clearly connected with 

 the sudden transmission upwards of immense quantities 

 of sugars in the spring. The depletion of the glandular 

 layer of the spring vessels will be made good from the 

 stores massed close by in the outer margin of the year-ring. 



We may imagine these carbohydrate glands forming a 

 sheath round the vessels to act somewhat as follows: In 

 spring their stored starch is rapidly brought into solution, 

 and the resulting sugars secreted into the vessels. The 

 solution in the tracheae acting osmotically through the 

 semi-permeable membrane formed by the outer tissues of 

 the root determines a flow of water from the soil to the 

 tracheae, and the resulting hydrostatic pressure is re- 

 sponsible for the exhibition of bleeding and root pressure 

 characteristic of the spring. This simultaneously forces 

 much of the air in the tracheae into solution, and raises 

 the sugars towards the buds. The observations recorded 

 show that the maximum concentration of the sugars in 

 the tracheae is simultaneous with, or just previous to, the 

 expansion of the leaves. The activity in transpiration of 

 the developing leaves is forwarded not only by the opening 



