radicle to bend away from the source of irritation.  In our experiments we followed Sachs’ plan, and sieves with seeds germinating in damp sawdust were suspended so that the bottom was generally inclined at 40o with the horizon.  If the radicles had been acted on solely by geotropism, they would have grown out of the bottom of the sieve perpendicularly downwards; but as they were attracted by the adjoining damp surface they bent towards it and were deflected 50o from the perpendicular.  For the sake of ascertaining whether the tip or the whole growing part of the radicle was sensitive to the moist air, a length of from 1 to 2 mm. was coated in a certain number of cases with a mixture of olive-oil and lamp-black.  This mixture was made in order to give consistence to the oil, so that a thick layer could be applied, which would exclude, at least to a large extent, the moist air, and would be easily visible.  A greater number of experiments than those which were actually tried would have been necessary, had not it been clearly established that the tip of the radicle is the part which is sensitive to various other irritants.

[Phaseolus multiflorus.—­Twenty-nine radicles, to which nothing had been done, growing out of a sieve, were observed at the same time with those which had their tips greased, and for an equal length of time.  Of the 29, 24 curved themselves so as to come into close contact with the bottom of the sieve.  The place of chief curvature was generally at a distance of 5 or 6 mm. from the apex.  Eight radicles had their tips greased for a length of 2 mm., and two others for a length of 1 ½ mm.; they were kept at a temperature of 15o — 16o C. After intervals of from 19 h. to 24 h. all were still vertically or almost vertically dependent, for some of them had moved towards the adjoining damp surface by about 10o.  They had therefore not been acted on, or only slightly acted on, by the damper air on one side, although the whole upper part was freely exposed.  After 48 h. three of these radicles became [page 182] considerably curved towards the sieve; and the absence of curvature in some of the others might perhaps be accounted for by their not having grown very well.  But it should be observed that during the first 19 h. to 24 h. all grew well; two of them having increased 2 and 3 mm. in length in 11 h.; five others increased 5 to 8 mm. in 19 h.; and two, which had been at first 4 and 6 mm. in length, increased in 24 h. to 15 and 20 mm.

The tips of 10 radicles, which likewise grew well, were coated with the grease for a length of only 1 mm., and now the result was somewhat different; for of these 4 curved themselves to the sieve in from 21 h. to 24h., whilst 6 did not do so.  Five of the latter were observed for an additional day, and now all excepting one became curved to the sieve.

The tips of 5 radicles were cauterised with nitrate of silver, and about 1 mm. in length was thus destroyed.  They were observed for periods varying between 11 h. and 24h., and were found to have grown well.  One of them had curved until it came into contact with the sieve; another was curving towards it; whilst the remaining three were still vertically dependent.  Of 7 not cauterised radicles observed at the same time, all had come into contact with the sieve.