SECRETION. 107 



ments which were instituted upon the subject, Brug- 

 mans and Coulon came to the conclusion that this se- 

 cretion at the end of the radicles was to be looked upon 

 as analogous to the discharge of fcecal matter from the 

 intestinal canal of animals, and that the matter secreted 

 was sometimes nourishing, and at other times detrimen- 

 tal to the growth of other plants. Oats were stated 

 to be killed by the secretions of Serratula arvensis, 

 Wheat by Erigeron acre, and Flax by Scabiosa arvensis, 

 etc., etc. Hedgwig denied the justice of these conclu- 

 sions, and in 1832, Macaire, at the suggestion of De- 

 candolle, made fresh inquiries into the subject, and de- 

 duced results which were generally admitted, though 

 they have been canvassed by some, especially by Unger 

 and Meyen, from whose notice upon this subject I shall 

 extract what follows: "Macaire," says Meyen, "ob- 

 served that the water in which he had placed some 

 plants, was polluted by different matters given off by 

 the ends of the roots ; and also that the water often had 

 a smell like some product to be found within the plants, 

 from which it was concluded that these matters were 

 separated by the roots ; but all along it was never sta- 

 ted whether the extremities of these organs were whole 

 or unhurt, the most important point in the experiments 

 being that they should be so. From another series of 

 experiments, but which are to be much doubted because 

 little or no attention was paid to the integrity of the 

 radicles, it was deduced that this power of separation of 

 matter by the ends of the roots served the purpose of 

 carrying off anything that could not be assimilated, or 

 was detrimental to the health of the plant. The doubts 

 already expressed were strengthened by the experiments 

 which Unger and myself instituted upon the question. 

 It is necessary throughout that the plants used in the ex- 

 periments should have had their roots developed in water, 

 as it is only in this way we can satisfy ourselves of the 

 unhurt and normal condition of the whole of them : we 

 made use of species of Lemna ; Unger grew them in so- 



