go BOTANICAL GAZETTE [FEBRUARY 
lished his theory of ‘‘heterogene induction.”’ He reviewed the 
earlier authors on the subject and described their conflicting results. 
According to Notw’s theory, if an organism is subjected to two 
stimuli, one gives impetus to the other which carries out the reac- 
tion. One stimulus only is responded to. There is no resultant | 
reaction toward the two stimuli. But when light and gravity 
work together, there is a change of geotonus due to light. 
Recently GUTTENBERG (2) studied the simultaneous effect of 
light and gravity, using seedlings of Avena sativa, Brassica Napus, 
Agrostemma Githago, and Helianthus. He used what he called the 
compensation method. He tried different light intensities. With 
the higher intensities the reaction was toward the light alone. By 
gradually decreasing the intensities, GUTTENBERG found a certain 
light strength which just equaled that of gravity, and he obtained 
a resultant reaction between the two. A little weaker or a little 
stronger light gave a resultant reaction, varying according to the 
intensity of the light. GurTrreNBERG considers this as evidence 
against NoLv’s theory of ‘‘heterogene induction.” 
RICHTER (5), working along the same lines as GUTTENBERG, 
came to quite different conclusions. For his experiments RICHTER 
“used Avena sativa, Vicia sativa, Vicia villosa, Brassica Napus, and 
Helianthus. He followed GuTTENBERG’s method and in each case 
carried on a set of experiments in pure air and a similar one in 
impure air. He concludes that GuTTENBERG did not establish a 
resultant reaction between the effect of light and gravity by means 
of his compensation method, but that the latter’s results were in- 
fluenced by the impure air in which the experiments were performed. 
GUTTENBERG (3) followed this by a second paper in which he still 
maintained his former views. In this he repeated his own experi- 
ments, taking precautions to work under pure air conditions. 
The experiments on simultaneous stimulation reported in this 
paper were performed with stimuli of the same kind, that is, they 
were light stimuli only. Before entering into a description of the 
work of simultaneous stimulation of Pilobolus, an account of some 
observations made on the reaction of a single sporangiophore of 
Pilobolus will be given. 
