?76 



being illuminated directly from above, the light first falls on 8 little 

 mirrors, which are arranged in a circle at equal distances round the 

 central sporangiophore at an angle of 45° with respect to the incident 

 rays. In this way the sporangiophore receives radially symmetricall}' 

 the same illumination on 8 sides. For various reasons — to be later 

 dealt with in greater detail — this arrangement was the more 

 satisfactory. 



The growth of the sporangiophore is always determined before 

 illumination by several observations at intervals of 5 to 10 min. 

 Whilst the variation in growth of ditFerent sporangiophores is consi- 

 derable, the growth of any individual one in successive minutes is 

 very uniform, especially when it is remembered with regard to the 

 figures found, (hat with observations at short intervals the error of 

 observation may be fairly lai'ge, because with weak, red light the 

 measurement must always be made fairly rapidly. The figures of 

 growth in the dark agree very well with those of Ekrera. In the 

 first series of experiments with 8-si(led illumination at 22° C. figures 

 were mostly found, which fell below the maximal growth according 

 to EiuiKRA, in the later experiments with unilateral illumination at 

 18°. 3 C, after the method of culture had been somewhat modified, 

 a value was general!}' found which agreed with the values found 

 by Errera during maximal growth. The eventual relative variations 

 in the rate of growth caused by the intluence of light were however 

 more important than the absolute rate. 



In the first experiments the plant was illuminated via the mirrors 

 on eacJi of the 8 sides with 14 metre candle power during 15 sec, 

 that is. eight tinier the quantity, which, given by one mirror only, 

 would have effected a decided curvature. When a growing cell 

 receives this amount of illumination, a very striking reaction of the 

 growth takes place. This reaction is all the more marked, the closer 

 the observations after illumination follow each other; for this reason 

 observations were made as far as possible every two minutes after 

 illumination. We then notice : 



1. that immediately after illumination growth still remains the same 

 for about 3 min. 



2. that after about 3 min. growth at once markedly increases to 

 reach a maximum 4l^I^ to 8 min. after illumination; with this 

 quantity of light the maximiun is usually not less than 2 or 3 times 

 the normal rate of growth. 



3. that afterwards the i-ate of growth again diminishes to its normal 

 value which is reached about 7 — 16 rain, after illumination. 



4. that often however the rate sinks to 10 to 307o below its 



