ETIOLATION. 



5?>S 



very strong and well-gtown Gourd-plant, furnished with about ten to twelve large 

 green leaves, the apical portion of the main stem is directed through a hole d, as small 

 as possible, into a large thick-walled wooden box K, and gently secured ; the box is 

 provided with a large well-fitting door. The figure shows how from the apical Itud 

 directed through rt', not only numerous leaves, tendrils, new shoots, and flowers (at B) 

 have been formell, but also a large fruit /; only these parts were considerably more 

 numerous than is shown in the figure. When the space became too small for the shoots 

 growing in the dark, I pushed the active terminal bud through a hole {e) in the roof 

 of the box out into the open air, and then made the necessary closure. The figure 

 shows how this shoot-bud which, originally directed into the box at d, had then 

 developed further in this for several weeks {B), on now being again exposed 

 to the light, has become quite normally developed again above the roof of the box at 

 C. The sojourn of this shoot-bud in the dark box was, so to speak, only an episode 

 in its life, during which it by no means- ceased to produce leaves, leaf-shoots,- tendrils, 

 roots and flowers in the usual manner. The foliage-leaves, which were of a 

 clear bright yellow colour, attained a considerable size, as seen. One of the 

 largest had a lamina 625 sq. cm. in area, while an average-sized leaf of the same 

 plant previously produced in the light, and dark green in colour, measured 825 sq. cm. 

 The leaves in the box attained on the average |-f the normal area, although they 

 w-ere only illuminated once every three or four days for a few minutes for the 

 purpose of observation, and produced no trace of chlorophyll. Still less was the 

 effect on the growth of the shoot-axes : the magnificent large tendrils were as 

 sensitive as it is possible for tendrils to be, the male and female flowers completely 

 normal in form, size, and colour, and, finally, the fruit/" when ripe weighed 4 kgr., 

 and possessed 195 seeds, a third of which were capable of germination ; and, in 

 a word, apart from the chemical process of greening and a few insignificant 

 disturbances in the growth of the foliage-leaves, as may be seen in the figure, 

 the growth in the dark, both in its embryonic and in its later stages, was essentially 

 normal, and that of the reproductive organs in particular quite normal. On now 

 noticing further that Gourd-seedlings in the dark exhibit the disease of etiolation 

 in the highest degree, and that their first leaves especially remain very small, the 

 above experiment teaches us that in this case it must be a matter not so much of a direct 

 influence of light on growth, as rather of the production of substances which bring 

 about growth subsequently. This follows also from the fact that the growth of the 

 organs enclosed in the dark cavity is so much the more vigorous and norm.al the 

 larger the assimilating leaf-area exposed to the light is, and the more intense the 

 light itself is outside the box. 



So long as nineteen years ago I obtained results similar to those with the 

 Gourd, with Phaseolus, Tropceohan (Indian Cress), and Ipomcia purpurea (Red 

 Bindweed). Of especial interest in all these cases is the unusually vigorous and 

 normal production of flowers and fruit, so long as the assimilation of the leaves 

 exposed to the light proceeds energetically. 



Since the products of assimilation of the leaves up to a certain extent 

 accumulate in the latter and in the shoot-axes, before they are made use of for 

 further growth, it is often possible to obtain vigorous shoots and flowers even in 

 the dark by simply placing entire strong plants (e.g. Tobacco, Wall-flower, kc>\. 



