278 



either end. Both the internodes and sheaths are striated, the former 

 more strongly so : the striae are usually about twenty in number in 

 luxuriant stems, but this number is liable to great variation, and 

 appears to depend solely on the size of the stem, always decreasing 

 towards its attenuated apex. The stems are hollow, and jointed or 

 divided by a strong transverse septum at each of the sheaths : the striae 

 of the sheaths correspond in number with those of the internodes, and 

 they terminate in an equal number of acute and elongate, but mem- 

 branous and often deciduous teeth. Under certain but unascertained 

 conditions these teeth become setiform and persistent, but in general 

 all trace of them is early lost, the upper margin of the sheath exhi- 

 biting a regular series of rounded divisions, uniform in number with 

 the striae of the stem. The basal portion of each sheath is black, 

 the central part whitish, and the upper part again black, the deci- 

 duous teeth excepted, the sides of which are membranous and trans- 

 parent. 



Sir Humphrey Davy detected in the stem of this plant an extraor- 

 dinary quantity of silex ; it is this that communicates the rough and 

 file-like character to its exterior, from which it derives its value as an 

 article of commerce. The silex appears in the form of minute crys- 

 tals, and is arranged with beautiful and perfect regularity. Under 

 the microscope we find on the stem numerous longitudinal series of 

 elevations, each bearing a cup-shaped depression in its centre, at the 

 bottom of which is placed a stoma. In the volume on Optics in 

 Lardner's ' Cabinet Cyclopedia,' Dr. Brewster has recorded that he 

 found each particle of silex to possess an axis of double refraction. 

 We are told by botanists that the quantity of silex is so great and the 

 particles are so closely set, that the M^hole of the vegetable matter may 

 be removed by maceration without destroying the form of the plant. 



I'he catkin is small, dark coloured, apiculate and terminal; its 

 scales are from forty to fifty in number, and each is impressed with 

 two or three vertical striae. Before the scales have separated in their 

 approach to maturity, these striae are continuous throughout the cat- 

 kin, even entering its terminal apiculus, which, in consequence, as- 

 sumes a polyhedral figure : they generally correspond in number with 

 the striae of the last internode, thus leading to the conclusion that the 

 catkin is a metamorphosed portion of the stem. 



Edward Newman. 



(To be continued.) 



