214 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



then takes place through the winter, culminating in the 

 vernal maximum. 



' 3. The vernal maximum coincides with the period of 

 greatest root pressure, and is simultaneous with or just 

 prior to the opening of the leaf buds. 



4. The rise in transpiration, initiated by the expanding 

 leaves and facilitated by the opening of the conducting 

 channels by root pressure, is largely responsible for the 

 dilution of the carbohydrates. The falling off and cessa- 

 tion of the transpiration stream in the autumn allows the 

 concentration again to rise. 



5. The conveyance upwards of sugars, of which sucrose 

 appears to be the most important, is a continual and 

 primary function of the tracheae. 



6. The sheath of wood parenchyma round the vessels 

 functions as a store from which sugars pass into the 

 rising transpiration stream. 



7. The relation of the medullary rays to these sheaths 

 supports the view that they convey the carbohydrates 

 from the bark to the glandular sheaths. 



8. The presence of large quantities of soluble carbo- 

 hydrates in the wood sap of roots is probably responsible 

 for root pressure and bleeding, by producing an osmotic 

 flow across the root cortex. 



9. The curves for the concentration of solutes in the 

 stem of the evergreen Ilex, and of the sub-evergreen 

 Cotoneaster, show smaller fluctuations than do those of 

 deciduous trees ; they have two cusps one about January, 

 and the other about August, in Ilex, and in February and 

 October in Cotoneaster. It is to be noted that in the case 

 of Ilex the buds expanded during the rise preceding each 

 of these cusps. 



10. The concentration of the carbohydrates is generally 

 greater in the trachea of the stem than in those of the root 



