357 



could be traced back from the place of cleavage, to varying depths. The 

 pro-cambial cells of the firo-vascular bundles were broadened like 

 bladders. 



The ducts thus exposed were simply broken off and, like the other ex- 

 posed surfaces, had absolutely uncolored walls at first. 



The separation begins to show itself in the rounding up and bending 

 outward of scattered cells in the basal tissue of the flower stalk, usually at 

 a short distance from the base of the bulb. Simultaneous with the begin- 

 ning of this convexity a swelling of the membranes of these cells appears 

 at the side where the curvature sets in. It is the striated middle lamella of 

 the cell walls which swells. Also, the swelling does not take place uni- 

 formly in the whole membranous layer, but in some places to a greater de- 

 gree than in others, hence the swollen, stripe-like areas have a knotted 

 course, in places showing constrictions. 



A bead-like irregular condition of the outer surface of the cell walls 

 in the cells lying next the cleavage surface seems worthy of attention. The 

 hemispherical, to nipple-shaped swellings correspond to those in the woolly 

 stripes in the apple core and take on a pure golden yellow color with chlo- 

 riodid of zinc while the rest of the membrane becomes intensely blue. This 

 disturbance sets in if, when growth starts, the hyacinths bulbs are given 

 at first too great warmth and too copious watering. The flower cluster, 

 not yet beginning to elongate, cannot utilize or absorb the water brought to 

 it by the increased root pressure. Thus an excess of water is accumulated 

 at the base of the flower stalk, whose cells elongate and weaken their 

 connection. 



A slower forcing of the hyacinth might prevent this condition. 



Twig Abscission. 



The small branches which, usually, together with their fully developed 

 foliage, are cut off from the main axis by some organic process may be 

 called abscissed twigs. This abscission takes place chiefly in the autumn, 

 yet it has been observed in summer (July) and as in leaf casting we 

 must take into consideration different causes for the same phenomenon. 

 All trees do not show this peculiarity and even those in which it appears 

 do not shed their branches every year\ nor do all of them do so. Young, 

 vigorous trees often do not shed, while older specimens, or those standing 

 on poor soil, in the autumn cover the ground underneath them with branches. 



The poplars- furnish the best known example. Their branches, often 

 meters long, with their swollen, hemispherically rounded joint-like abscission 

 surfaces, smooth and shining like velvet in damp weather, show most clearly 

 that the branch is not loosened by a forcible tearing of its component parts, 

 but by a separation of certain tissue zones preceded by internal organic 

 processes. 



1 Borkhausen, Forstbotanik I, p. 294. 



- K. Muller, Hal., Der Pflanzenstaat, p. 532, gives an illustration of this. 



