BOTANY. 305 



If this view were adopted, we should have to cut- off many classes 

 of animals from the possession of sensibility, and by so doing, brinw 

 them into still closer connection with plants. But then arises the 

 question, Whence the contractility of plants ? It is here that Cohn's 

 admirable memoir 1 throws a flood of light. He has discovered, that 

 in at least one portion of a plant, the stamen of the Centaurea, 

 there exists a tissue which presides over the phenomena of contractility; 

 and he naturally infers that in all other supposed cases of plant-con- 

 tractility a similar tissue will be present. 



We cannot pretend here to condense the numerous observations 

 and rigorously-conducted experiments by which he establishes his re- 

 sults. Curious readers must consult the original. We give the results. 

 The stamen of the Centaurea is excited by the mechanical, chemical, 

 and electrical stimuli which excite muscles ; when excited, it contracts 

 in the same way as a muscle, describing the same curve, when, after 

 reaching its maximum, it begins to relax again. Like the muscle, it 

 becomes tired by contraction, and recovers its exhausted force only by 

 repose. Like a muscle, it is excited by a weak galvanic current, and 

 rendered tetanic by a strong current. Like a muscle, it exhibits three 

 properties, first, that of being excited by stimuli ; secondly, that of 

 changing its form on being excited ; thirdly, that of transmitting every 

 stimulus under its correlate as motor-force to neighboring parts. 



The importance of this discovery will not be overlooked. If, as one 

 can only infer, the phenomena observed in other plants should be 

 found equally reducible to a similar tissue of contractile cells, we shall 

 have a beautiful explanation of many biological phenomena now very 

 obscure. The reader will remark that we have, throughout, for cer- 

 tain purposes of our own, spoken of the " muscular tissue" where Cohn 

 uses the term "contractile tissue." .It is true, to remove any miscon- 

 ception, which might arise from this use of the term, by muscular tis- 

 sue must not be understood the special organs named " muscles " in 

 animals, which are formed of muscular tissue, and several other tissues. 

 Nor, even, must it be understood as indicating a tissue of muscular 

 fibres, such as we find in the higher animals ; but simply a tissue of 

 contractile cells. It will prevent any misconception, if we remember 

 that what are called muscles, or muscular tissue in the simpler animals, 

 are nothing but contractile cells ; and a diagram of the muscles in a 

 fresh-water polyp would differ very little from a diagram of a cellular 

 tissue in plants. 



THE DESTRUCTION OF NOXIOUS INSECTS BY MEANS OF THE PY- 

 RETHRUM (PERSIAN INSECT POWDER). 



M. Willemot, of France, has recently published, in the Technologist, 

 an interesting paper, on the cultivation and use of the Pyrethrum (P. 

 carneum), of which the celebrated Persian powder for the destruction 

 of insects is prepared. This powder was first introduced into France 

 in 1850, and came exclusively from districts of Persia and the Caucasus. 

 Within a few years, however, the plant itself has been introduced into 

 France, and at the present date is cultivated successfully and in large 

 quantities. It is described as a small perennial shrub, from twelve to 



1 F. Cohn; Contractile Gewebe in rflanzenreiche, Breslau, 1862. 

 26* 



