IRRITO-COXTRACTJIJTY IN PLANTS. 207 



the protoplasm will almost certainly contract, and the leaflets 

 will fall. But as evening advances, lowering of the air temper- 

 ature, radiation from the leaflets, — and still more importantly, 

 I believe, — the cutting off of the light stimuli along with 

 reduced temperature of the soil, will all act steadily, and the 

 leaflets, newly recovered from the parathermotropic state, will 

 pass soon after into the nyctitropic state. 



To distinguish the relation to altered environmental surround- 

 ings, we speak of night-sleep or nyctitropism, and heat-sleep or 

 parathermotropism, but fundamentally both are due, we believe, 

 to one and the same fundamental peculiarity of the protoplasm, 

 though we cannot stop here to discuss Brucke's assertion of a 

 difference owing to difference of tension. 



A distinct exception to this principle, however, seemed to be 

 involved in Pfeffer's statement first made in \)\9^ Pflanzcn physi- 

 ologic, and afterwards extended into a paper published in his 

 Laboratory Jon nun I. He there asserted that sensitive plants like 

 Mimosa, Oxalis, Diojlcea, etc. differed fundamentally from such 

 stem or leaf parts as tendrils and from the hairs of Droscra, 

 in that the former were sensitive to impact, the latter only to 

 contact. So many cases of summation of stimuli being needed 

 to effect movement had been met with by me, that I deter- 

 mined to ascertain experimentally, whether coiling of a tendril 

 was not due to a summation of distinct impacts combined, of 

 course, with circumnutation of the organ. Fortunately, I had 

 fine plants of those he experimented on growing in my garden 

 or within easy reach. Pfeffer states that the long, graceful 

 tendril of Sicyos — the bur cucumber — only coils into a helix 

 if subjected to contact rubbing. I first selected a primary 

 tendril of EcJiiiiocystis lobata, that was 5^ inches long and 

 faintly incurved at its tip, as is usual. Thirty delicate 

 mechanical shocks were given in series of five at intervals of 

 10 seconds, and spread over i^- inches of the tip. Soon 

 after delivery of the second five — i.e., within 25 seconds — 

 there was a distinct curving of the irritated region. In 6 

 minutes the tendril had curved sharply through f of a circle, 

 and in 23 minutes through i^ of a circle. It was first 

 irritated at 7.21 p.m., and when examined i^ hours later 



