614 Proceedings of the Royal Irish Academy. 



tition under new conditions. In the present communication I shall 

 confine myself to the statement of experiments made with a variety of 

 the tobacco plant {Nicotiana longiflora). The seeds were obtained 

 from Messrs. Yeitch & Sons, and aiiorded a good crop of young 

 plants, which were removed from the seed-bed, and potted singly in 

 very sandy mountain loam, of rather poor quality, the aim being to 

 give the plants no more nourishment than was absolutely necessary to 

 ensure moderate development. When the plants were shifted into 

 four-inch pots, they were allowed to become thoroughly established, 

 and the experiments commenced. 



Several sets of three healthy plants were picked out, and the 

 members of each set were as nearly as possible in the same stage of 

 development, i. e. they were of the same height, had an equal num- 

 ber of leaves, and equally strong stems. Each set was subjected to 

 the same treatment ; but it will conduce to clearness if I trace that of 

 a single set. 



The treatment pursued was the following : — 



No, 1. was watered with Vartry water only, when necessary. 

 Jfo. 2 was watered twice each week with a solution of 0'5 gram 



of pure thiocarbamide in 250 c.c. of water : at other times 



it was treated as 'Eo. 1. 

 iNo. 3 was watered twice each week (unless otherwise stated) with 



a solution of 0"5 gram of pure ammonium sulphocyanate in 



250 c.c. of water. 



The plants were under glass, but so placed as to get equal light, 

 and to prevent any undue tendency to drawing up or " spindling." 



The first to show any effects was !N"o. 3 {i. e. that treated with 

 the sulphocyanate) ; at the third treatment with the solution the 

 growth was checked, and the plant seemed not only to stop develop- 

 ment, but even to shrink in a curious way ; the leaves began to droop, 

 and became rather sickly in colour. The fourth application only 

 intensified the symptoms of plant-poisoning by the sulphocyanate, 

 hence the treatment was stopped, and the soil well washed out by 

 percolation of pure water : after this the plant recovered somewhat, 

 and recommenced growth ; but it received another dose, which again 

 checked development. Washing the soil was repeated, and another 

 rest allowed. This treatment was continued for nearly three months, 

 up to the 1st of December, when it presented a very miserable 

 appearance, and was in the condition stated in the Table. This plant 

 was then removed from the soil, and dried. 



There is no doubt that I could have killed this plant at any time 

 by continued doses of the sulphocyanate, for corresponding plants of 

 other sets so treated with the salt were destroyed in a few weeks. 



K'o 2 plant («'. e. that treated with the solution of thiocarbamide) 

 soon gave evidence that it felt the effect of its dose, but the result 



