168 CHARLES DARWIN. 



of Plants' (1880). This last volume, in which he was assisted by 

 Mr. Francis Darwin, has been so recentlj^ published, and some of 

 its conclusions are still exciting so much controversy, that only a 

 brief reference to the leading results will be needful. Mr. Darwin 

 shows that, so far fi-om the power of apparently spontaneous 

 movement being an exceptional phenomenon, every growing part 

 of every plant is apparently continually ch^cumnutating, though 

 often on a small scale. Even the stems of seedlings, before they 

 have broken through the ground, as well as then- buried radicles, 

 circumnutate, as far as the pressure of the surrounding earth 

 permits. From this modified circumnutation, which is always 

 present as long as growth lasts, and even continues after growth 

 has ceased wherever there are pulvini, are derived all those 

 movements due to hypnast}^ and epinasty, the revolving nutation 

 of climbing plants, the nyctitropic or sleep-movements of leaves 

 and cotyledons, and those excited by light and gravitation, helio- 

 tropism and geotropism. There are other movements, like those 

 of the leaves of Mimosa and of the tentacles of Drosera, which cannot 

 be traced to this law. Mr. Darwin has frequently pointed out, in 

 the course of his writings, the strong resemblance which exists 

 between some of these movements and those which characterise the 

 lower animals. Speaking of the sensitiveness of the tips of radicles, 

 he says : — " It is hardly an exaggeration to say that the tip of the 

 radicle, thus endowed, and having the power of du-ecting the 

 movements of the adjoining parts, acts like the brain of one of the 

 lower animals ; the brain being seated within the anterior end of 

 the body, receiving impressions from the sense-organs, and dkecting 

 the several movements." 



Mr. Darwin's 'Insectivorous Plants' (1875) is perhaps, more 

 completely than any other of his works since the ' Origin of Species,' 

 the text-book of the subject on which it treats. He here deals with 

 the remarkable x^henomenon of the aggregation of protoplasm in 

 the tentacles of Drusera, and the extraordinary sensitiveness of 

 these tentacles to contact w^ith any nitrogenous substances in 

 quantities so minute as to defy the most delicate chemical tests. 

 And again, the points of contact between the animal and vegetable 

 kingdoms are brought out in the power possessed by the Droseracea 

 and other insectivorous plants of dissolving animal matter by the 

 aid of a special secretion, which contains an acid, together with a 

 ferment almost identical in nature with pepsin, by the aid of which 

 a true process of digestion is carried on. The last of Mr. Darwin's 

 writings, consisting of his papers presented to the Linnean Society 

 so recently as March 16th of the present year, on " The Action of 

 Carbonate of Ammonia on the Roots of Certain Plants," and on 

 "The Action of Carbonate of iVmmonia on Chlorophyll-Bodies" 

 still further illustrate the phenomena of aggregation to which his 

 attention was dh-ected in these researches : an abstract of these is 

 given in this number of the 'Journal of Botany.' 



