Chap. II] PERIODIC PHENOMENA IN TEMPERATE ZONES 435 



is however occasionally converted into starch (transitory starch). The 

 path of this stream of glucose is always the same. It is determined in 

 the leaves by the elongated parenchyma-cells of the nerves and petiole, 

 and in the axes is confined to the cortical parenchyma. From the cortex 

 the stream flows horizontally into the wood, where the parenchyma-cells 

 gradually fill with starch, whilst the vessels retain as such the glucose 

 they have received from the parenchyma. There is no descending current 

 of assimilated matter in the wood. 



The commencement of leaf -fall indicates in the tree the moment at which 

 the tree contains the greatest amount of assimilated matter {autumnal maxi- 

 mum). From now onwards up to the beginning of the next vegetative 

 season a continual diminution in that amount takes place, at first slowly, 

 but finally very rapidly. 



Immediately after reaching its autumnal maximum, which is also 

 specially that of starch (autumnal starch-maximum), the assimilated matter 

 within the axes is distributed in the following manner : — The parenchyma of 

 the cortex and of the medullary rays is rich in starch and glucose ; the 

 cambium contains neither. The wood contains much starch but no glucose 

 in its living cells, much glucose but no starch in the vessels. The medul- 

 lary sheath is rich in both substances ; on the other hand they occur in 

 the pith here and there only. 



Shortly after leaf-fall the starch completely disappears from the cortex, 

 as it is converted partly into glucose and some fat, partly into some still 

 unknown bodies (species of sugar). The wood is somewhat poorer in 

 glucose than during summer, but shows no perceptible diminution in the 

 quantity of starch it contains. 



The buds at the time of the starch-maximum contain no glucose, but 

 the scales are rich in starch, and the pith still more so. The embryonic 

 organs are devoid of starch and glucose. 



Towards the end of winter, even before any externally visible changes 

 indicate the commencement of the vegetative season, activity commences in 

 the interior of the tree. The cortex free from starch becomes again filled 

 with this substance, clearly at the cost of the glucose and of the unknown 

 bodies formed during autumn (spring starch-maximum). This condition 

 is only of short duration. The starch is again partly converted into 

 glucose and this flows into the vessels. In the vessels the current of sap 

 sets itself in motion and provides the buds — hitherto poorly supplied with 

 water and nutriment — with water and glucose. 



Even in the buds, movements in the reserve-material have taken place 

 during the winter-sleep. The starch has left the pith, where it was at 

 first so abundant, and has now accumulated in the embryonic leaves and 

 flowers, from which hitherto it had been absent. It is reserve-material, and 

 just suffices for the first stages in the flushing of the buds, that is, up to 



F f 3 



