NATURE 



529 



THURSDAY, APRIL 10, 1902. 



SENSE ORGANS IN THE VEGETABLE 

 KINGDOM. 

 SinncsorgMie in Pflanzenrcicli zur Perception iiiec/uui- 

 ischcr lieise. Von Dr. G. Haberlandt, 0.6. Professor 

 an der Universitat Graz. Pp. viii + 163 ; 6 plates. 

 (Leipzig : Engelmann, 1901.) Price <)s. net. 



MR. HUXLEY has truly said' that "perhaps the 

 most remarkable service to the philosophy of 

 biology rendered by Mr. Darwin is the reconciliation of 

 teleology and morphology, and the explanation of the 

 facts of both, which his views offer." Prof. Haberlandt 

 is a devoted adherent to the school of evolutionary tele- 

 ology ; one of his earliest publications (in 1877) was a 

 study of the protective adaptations of seedlings, and the 

 desire to understand the meaning of every detail of 

 plant-structure is still the key to his activity. It has 

 led him, following the footsteps of Schwendener, to 

 specialise in what he names physiological anatomy, 

 which might with equal propriety be termed teleological 

 or adaptive anatomy. Haberlandt's book,- in which he 

 elucidates the minuter structure of plants from this point 

 of view, is a recognised classic and is found in every 

 botanical library in the world. The present work will, 

 we think, only add to his reputation as an investigator. 



The title of his book, " Sense Organs in the \'egetable 

 Kingdom," &c., would by itself suggest the school of 

 thought to which Haberlandt belongs, and on his first 

 page he asserts that the plants have specific forms of 

 irritability which are completely analogous to the senses 

 of animals. This school, which puts side by side the 

 reflex movements of plants and animals, dates (in its 

 modern development) from the writings of Pfefifer and 

 Sachs in Germany, and from the pul)lication of " The 

 Power of Movement in Plants " in this country,' and is 

 now generally accepted. 



Haberlandt's book deals with the reflexes called forth 

 by tactile stimulation, more especially with one branch 

 of the subject, namely, the mechanism which localises 

 and intensifies the touch. The means by which the dis- 

 turbance, thus originated, is transmitted to the motor 

 organs is for the moment of secondary importance with 

 the author. 



Haberlandt begins with the following definition : — 



" Sense organs, or organs of perception, are those struc- 

 tural contrivances which contribute to the reception of an 

 external stimulus, and show a more or less striking 

 correspondence between structure and function." 



According to this broad definition, the sense organ need 

 not itself possess the quality of percipience. The essen- 

 tial characteristic is an arrangement for a sudden " de- 

 formation" of the ectoplasm in sense-cells. But certain 

 plant-hairs and bristles are called sense organs, although 

 they merely act like the vibriss;e of animals, that is to say 

 like levers, the act of percipience occurring in the sensi- 

 tive tissues in which they are imbedded. Haberlandt 

 practically narrows his definition by applying the term 



1 " Life and Letters of Charles Darwin," ii. p. 201. 



*-i '* Physiologische Pflanzenanatomie." 1st lidit. 1884, 2nd Edit. 1896. 

 (Leipzig : Eneelmann.) 



^ The earliest popular statement of this point of view was published by 

 the writer of this notice in Natuke, 1878, vol. xvii. pp. 390, 411, &c. 



NO. 1693, VOL. 65J 



Stimulator to the purely mechanical parts of sense 

 organs, a terminology which seems to us of rather 

 doubtful value, more especially as stimulators seem to 

 graduate into sense organs in the narrower sense. 



The simplest class of sense organs contains what the 

 author calls Fiihlpapilleii or Tactile-papillae. These, as 

 they occur in the stamens of Opuntia, &c., have been already 

 described by Haberlandt in his" Physiologische Pflanzen- 

 anatomie" ; the present book demonstrates the remarkable 

 fact that tactile papilla: occur in many different organs 

 and in widely distinct natural orders — a state of things 

 with which we are familiar in many adaptive structures, 

 and which never fails to interest us. The tactile papilla 

 in Opuntia consists of a small conical projection from 

 an epidermic cell, into which runs a promontory of proto- 

 plasm. The fact that the papilla projects above the 

 general surface renders it liable to be touched by the 

 visiting insects, and the thin walls of the apical half of the 

 papilla allow deformation to result from contact. The 

 papilla? in this instance are not, however, very sensitive 

 to simple contact, for if the stamens are gently rubbed 

 they curve but slightly, whereas if the filament is forcibly 

 bent at the same time, as would be the case when an in- 

 sect visited the flower, the reaction is greater. This is 

 only one instance of the care with which Haberlandt has, 

 throughout, distinguished the reaction due to contact 

 that is produced by bending of the whole organ. In this 

 case, and also in Portulaca, it seems that if the filament 

 is merely stroked the needle sHps over the papillie with- 

 out seriously affecting them, but pressure at right angles 

 to the filament deforms the wall of the tactile papilla 

 and also bends the filament. 



In the filaments of Berberis, the tactile papilla is of 

 still simpler structure, being formed by the convex projec- 

 tion of the whole outer wall of an epidermic cell. The dis- 

 tribution of the cells corresponds with that of the region 

 sensitive to contact, and here in contrast to Opuntia a 

 slight touch, which produces no bending of the filament, 

 is sufficient to call forth the reaction. It is true that forcible 

 bending of the filament also has an effect, but the move- 

 ment produced is incomplete ; it is interesting that the 

 motor machinery should respond less to direct deforma- 

 tion of its own constituent cells than to a minute change 

 of form in the cells specialised as sense organs. 



The tactile cells in Berberis differ from the non-sensitive 

 ones in being richer in protoplasm, in containing orange 

 chromoplasts and starch grains. The exposed projecting 

 wall of the sense cells is not thin as in Opuntia or 

 Portulaca ; the disturbance produced by contact is appar- 

 ently due to a curious thinning away of the outer wall 

 where it meets the radial walls. This hinge-like 

 mechanism must allow a ' localised deformation of the 

 ectoplasm to occur ; the cell is, in fact, like a box with 

 strong but loosely fitting hinged lid, the hinges being the 

 region where deformation especially occurs. The same 

 type — a bulging epidermic cell with a hinged connection 

 to the radial walls — occurs in Abutilon in a different 

 natural order. The irritable stamens of Helianthemutn 

 are worthy of notice, from the absence of all definite 

 sense organs. Haberlandt assumes that the delicacy of 

 the epidermis renders superfluous any special arrange- 

 ments ; and he compares the filaments to those tendrils 

 in which histological adaptations are absent. 



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