200 



SCIEXCE-GOSSIP. 



A few only of the differences that exist between 

 these two plants can be enumerated here. Drosera 

 feeds on good flying insects which are caught by its 

 viscid secretion. Dionza only catches those that 

 cannot readily take flight. Darwin found that 

 none of the Droseraceae were forced to close then- 

 leaves during a shower of rain or during a very 

 high wind. The presence of the set of marginal 

 spikes round the edges of the lobes in Dionsa gave 

 the great naturalist much food for reflection. 

 He would not believe that they were of no use to 

 the plant, for in Nature we seldom find any fully- 

 developed structure rendering no service to the 

 organism to which it is attached. 



By patient and continued observation he found 

 that small insects can escape during the slow closing 

 of the lobes, but that moderately large insects are 

 pushed back again on their trying to escape from 

 the prison, until the spikes go on crossing till the 

 edges of the lobes come into contact with each 

 other. It would be useless for the plant to remain 

 closed on minute insects for several days, and then 

 spend several days in recovering its sensibility. It 

 would be much better for it to allow all the little 

 ones to escape. 



Let us see what happens to a fly when it alights 

 on a leaf of Dions a. It will not be long crawling 

 about before it touches one of three pointed 

 filaments which project from the surface of each 

 lobe. As soon as one of these filaments is touched, 

 the fact is communicated all over the plant, 

 and both lobes begin to close over their prey, 

 which is soon crushed by the vigorous contraction 

 of the above-mentioned lobes. 



Dr. Burdon Sanderson, the distinguished physio- 

 logist, came to the conclusion some years ago that 

 there must be some relation between muscular 

 contraction and plant movement, and he made 

 several experiments in order to show that the 

 phenomena of contractability in Dionaa agreed with 

 those in animals, and that when a leaf of Dionaa 

 contracted, effects were produced similar to those 

 which occurred when a muscle contracted. Dr. 

 Sanderson had not gone very- far in his experiments 

 before his results were called into question by two 

 German professors, Munk and Kunkel. The latter 

 said that the electromotive phenomena manifested 

 by Dionaa were dependent on the distribution of 

 water in the tissues, and so have nothing in common 

 with the electromotive phenomena of muscle and 

 nerve. After more experiments, Dr. Burdon 

 Sanderson was able to demonstrate that, though 

 electrical disturbances took place when the leaves 

 of Dionaa were caused to move just as they 

 occurred when a muscle contracted, the mechanism 

 of plant motion was entirely different from that of 

 animal motion. In both cases work springs out of 

 the chemical transformation of material ; the differ- 

 ence lies in the rate or intensity of the fundamental 



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 It is well known that the sensitive plant moves 

 when the cells undergo a certain diminution of 

 tension or expansion . The loss of ten sion is effected 

 by the discharge of water. In an unexcited state 

 the plant is filled with water, but when it is excited 

 it discharges liquid. Pfeffer made the f mous 

 discovery that when the leaf-stalk is cut away from 

 the motor organ, a drop of fluid appears at the cut 

 surface at the moment that the latter bends down- 

 ward on excitation. 



"When a muscle contracts, it does not diminish 

 in volume, but when the filaments of Dionaa 

 contract, they diminish in bulk by the discharge of 

 liquid from the cells. A fanciful American 

 observer alleged that Dionaa could distinguish 

 between living animals and inanimate objects. 

 He said that he had tried to fool the plant by 

 offering it dead insects, but that it was able to close 

 its lobes only when it felt the insect walking about. 

 This statement must appear absurd to all who have 

 read Darwin's work and who have had opportuni- 

 ties of studying the plant, either in its native haunts 

 or at Kew. These are the half-hearted methods of 

 observation that do so much to discredit botanical 

 science in the eyes of the world. Darwin's words 

 on this point must settle the question definitely. 

 He says that it is scarcely possible to touch the 

 filament ever so lightly with any hard object, 

 without causing the lobes to close. The Droseracea 

 have been divided into three groups. In the first 

 are Drosophyllum, Roridvla and Byblis, which all 

 catch insects by a viscid fluid secreted from 

 their glands. In class two we find Drosera, which 

 uses the same means as the above, but differs from 

 them by the movement of its tentacles. 



In the last group are Dionaa and AMrovanda, 

 which entrap their victims by the closing of the 

 blades of their leaves. To exhaust the information 

 obtainable on the insectivorous plants would be 

 impossible, except in a large volume. The object 

 of these lines lias been but to awaken interest in 

 this fascinating subject. 



80, Elsham Road, London, W. 



A New Rotifer. — Mr. John Hood, F.R.M.S., 

 describes a new species of rotifer, Sacculus mirassis, 

 Sp. Nov., in the " International Journal of Micro- 

 scopv ' ; for October. He has occasionally found it in 

 the waters of Loch Lintrathen for some years past, 

 and during the exceptionally warm weather in May, 

 June and July of last summer (1893), it was very 

 prolific in the domestic water-supply of Dundee. 

 The article is illustrated by a plate. There is also 

 a useful article in the same part, by Professor 

 V. A. Latham, on methods and formulae used in 

 the preparation and examination of the normal 

 ar.l zz.'.'-'.'.-.-f.Zc.'. i-:r:: : ::' 'z'.zzt. 



