E^ect of Arsenic Compounds 59 



(d) Physiological considerations. 



The physiological action of arsenic compounds on plant life early 

 attracted the attention of investigators. Chatin (1845) put forward 

 some rather curious and unexpected considerations with regard to 

 this action. He stated that the effect of arsenic on plant growth 

 is determined more by the constitution and temperament of indi- 

 vidual plants than by their age, and that apparently difference in 

 the sex of plants is of no significance. The chief determining agent, 

 however, is the species, and Chatin found that as a general rule 

 Cryptogams are more sensitive than Phanerogams, and Monocotyledons 

 than Dicotyledons, as is shown by the fact that under treatment the 

 former perish first. Some extreme exceptions exist, though, as Mucor 

 mucedo and Penicillium glaucum will grow on moist arsenious acid, 

 whereas leguminous plants are killed by an arsenical solution in a few 

 hours. Chatin held the view that elimination of the poison succeeded 

 its absorption, and that this elimination is complete if the plant 

 lives long enough. Here again the species exerts a great influence 

 on the excretory functions of the plants. Lupins and Phaseolus are 

 presumably able to eliminate in six weeks all the arsenious acid they 

 can absorb without dying. Most Dicotyledons need 3 — 5 months, 

 while Monocotyledons retain traces of poison for six months after its 

 absorption. Lichens are said to eliminate it more slowly still. Again, 

 woody species are longer in freeing themselves than herbaceous, 

 and young plants carry out the elimination more easily than old 

 plants. The excretory function is influenced by other physiological 

 factors such as dryness and season. The toxic effects and elimination 

 are supposed to act inversely and parallel, the absorbed arsenious acid 

 combining with alkaline bases, making a very soluble salt which is 

 excreted by the roots. Calcium chloride is given as the antidote to 

 arsenious acid, all soluble acid being "neutralised" by it. This view 

 of the elimination of arsenic apparently did not gain much support, as 

 no further references to the matter have so far come to light. In view 

 of the work of some modem investigators (Wilfarth, Romer and Wim- 

 mer) on the excretion of salts by plant roots, the idea may prove of 

 fi-esh interest. Chatin also found that moving or still air influenced the 

 working of the poison, indicating that the external physical conditions 

 affect the toxic action considerably. Nearly forty years later Nobbe, 

 Baessler and Will found that, if transpiration were hindered by 

 placing plants in a dark or moist room, it was possible to keep 



