504 MANUAL OP BOTANY 



and a regulating and controlling part which can co-ordinate the 

 response to stimulation, or can initiate movements, &o., in its 

 absence. In the higher animals these are well differentiated 

 from each other ; we have the sense organs and the afferent 

 nerves ; the efferent nerves, connected with the motor and other 

 mechanisms ; and the nerve-cells which possess the co-ordinating 

 power. In the much less differentiated plant-body the first two 

 of these at least are recognisable. If we compare the sense 

 organs of the animal with the sensitive parts of the plant, we 

 find a certain correspondence, thougli it must not be pressed 

 too far. The power of sight i« very complete in the higher 

 animals, in consequence of the highly differentiated character 



Fig. 1194. 



fiff. 1194, Continuity of tlie protoplasm of contiguous cells of the endosperm 

 of a Palm seed {Benlinckw }. ir. Contracted protoplasm of a cell. &. A 

 group of delicate protoplasmic fibrilspassingtbroughapit in thecell-walJ. 

 (Higbly magnified, after G-ardiuer ) 



of the eye. In the lower animals it becomes less and less 

 perfect, till in some it goes probably little further than the 

 power of appreciating light. This power we have seen to be' 

 possessed by certain parts of the young seedlings of various 

 plants in a very high degree, and by other organs to a less 

 extent. The sense of touch may be compared with the power 

 of responding to the stimulus of contact shown by tendrils and 

 by the tips of roots; the muscular sense, or power of appre- 

 ciating weight, is not dissimilar to the property of responding 

 to the force of gravity, while the chemiotactic behaviour of the 

 organisms described above suggests a rudimentary power of 

 taste or smell, or both. 



The conduction of the impulses received is due in animals 



