230 LIFE IN DEATH, AS MANIFEST 



sidering how this comes to pass, we are brought face to face with 

 another of those marvels of anticipation in nature which so 

 deservingly astound us, and land us ultimately in life-mysteries 

 which laugh at all our theories of Biology. What, for instance, 

 do we know of the processes whereby, in the dark and under 

 water, the eyes of Libellula are fashioned, with their four-and- 

 twenty thousand facets ? We can only say, with Topsy, that we 

 suppose they grow. And it is a no less remarkable work of 

 nature which underlies by anticipation the autumnal leaf-fall. 



Long before the leaf shows any signs of dissolution there are 

 internal indications of a coming change. These consist in the 

 development of two new cortical features at the base of the petiole, 

 viz., Periderm, and the Absciss layer. The latter is a layer of special 

 cells — smaller, more rounded, and more loosely coherent than 

 the ordinary cortical parenchyma — which is formed immediately 

 beneath the base of the leaf-stalk. This is not always equally 

 easy to make out distinctly, yet it may be plainly observed in the 

 following : — ^scidus Hippocasta?nim (Horse Chestnut), Rohmia 

 Pseudacacia (bastard Acacia), Populus dilatata. If access to 

 Gym?iocladus canadensis (Kentucky Coffee-tree) be possible," it is a 

 specially suitable subject for illustration, and maybe experimented 

 on. Thus, if strong leaves are placed in the dark and damp, an 

 Absciss layer is formed at once under the base of the leaflet-stalks, 

 so that in about two days the leaflets drop off on the slightest 

 touch. — (cf. Strashurger^ Eng. tr. Ed. by Hill house.) 



Almost equally good subjects for investigation are Ailanthus 

 glandulosa^ Eraxinus excelsior., and Juglans regia. For ordinary 

 students, the Horse Chestnut is best, both because of its easy 

 accessibility and plainness of demonstration. The accompanying 

 sketch is taken from a petiole insertion last autumn, and is fairly 

 typical. (PL XV., Fig. i.) 



When the Absciss layer is fully developed, the leaf drops off 

 with a very small amount of mechanical disturbance, thus especially 

 through the force of the wind. 



Sachs also interestingly states how temperature effects a 

 similar result. The cells of the Absciss layer being loose and rounded, 

 allow of the presence of more water than usual in their interstices. 

 Thus with the first frosty nights of October, a thin plate of ice 



