178 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lviii. 



species were more prone to become " double " than those 

 of the Dalmatian. When an insect was exposed to the 

 action of the powder it was speedily paralysed, but in a 

 few minutes seemed to slightly revive again. Soft-bodied 

 insects, such as house flies and bees, were speedily killed, 

 but hard-bodied insects, like beetles and cockroaches, 

 resisted its action for a much longer time, and were not 

 killed till after 50 or 60 hours exposure. Though not 

 dead they were, however, rendered helpless, and could be 

 easily captured and destroyed. The insecticidal properties 

 of the flowers had been attributed to various constituents, 

 and their toxic action was not thoroughly understood. 

 They contained a small percentage of a volatile oil, which 

 gave them their characteristic " tea-like " odour and slightly 

 aromatic taste. It had been stated that the volatile oil 

 was the active constituent, but that had not been proved. 

 Schlagdenhauffen and Keeb found in the flower-heads a 

 poisonous volatile acid, chry&anthemic acid, and also a 

 poisonous non-volatile acid, pyrethrotoxic acid, to both of 

 which they ascribed the insecticidal properties of the 

 powder. 



The specimens shown consisted of the three grades met 

 with in commerce, namely : — 



1. The closed flower-heads. These were the best 



quality, and by grinding these the finest and most 

 powerful insect powder was obtained. They were 

 worth, in the wholesale market, about £5, 16s. 

 per cwt. 



2. The half-closed flower -heads. From these a second 



grade of insect powder was obtained. They were 

 less aromatic and less powerfully insecticidal 

 than the preceding grade. They were worth 

 about £4 per cwt. 



3. The open flower-heads. These were the lowest 

 •commercial grade, and worth only about £3 per 

 cwt. 



Professor Bayley Balfour directed the attention of the 

 Society to a paper in the " Kew Bulletin," giving an 

 account of the production of citric acid, on a commercial 

 scale, from sugar, by the agency of a form of Penicillium. 



