114 HALF-AN-HOUR 



the play of elective affinity between the two edges of a scratch ! 

 Exquisite mountings might be obtained by delicate geometrical 

 patterns cut with the diamond-writing machine. Who will try 

 this ? 



Ophiocoma neglecta. — Members visiting Southend, Margate, 

 Ramsgate, Deal, Dover, etc., and probably any of our sandy sea- 

 shores, would find a search for these richly rewarded. The 

 Echmoder^nata generally furnish no end of instructive and 

 beautiful preparations. To know what to look for, and how to 

 look, read Forbes' " British Star-Fishes," and then set to work. 



Calcedony is a type of a good class of objects, from which 

 much interest and instruction are to be derived, namely — as illus- 

 trating microscopically the intimate structure of geological and 

 mineralogical specimens. The physical conditions under which 

 they were formed present problems of the grandest order. David 

 Forbes, whose writings are unfortunately scattered through various 

 periodicals (" Popular Science Review" and "Proceedings of the 

 Geological Society " are the most accessible), is the pioneer and 

 almost the only worker. I must warn my fellow-members, how- 

 ever, that such slides are at the present very difficult to prepare, 

 from their extreme hardness, and most of us will prefer paying a 

 visit to the opticians, and choosing for ourselves an illustrative 

 series from their admirable collections. 



Those who wish to learn about Calcedony must read J. Morris 

 on " The Gems and Precious Stones of Great Britain," in " Popu- 

 lar Science Review," April, 1868, p. 123. 



Seeds of Typha latifolia have evidently been mounted by a 

 novice, from a specimen in excellent condition. One, two, or, at 

 most, three seeds should have been picked out carefully with the 

 forceps, and laid side by side, instead of the confused mass here 

 presented to the eye, from which it is tedious, even for an expert^ 

 to gain the facts intended to be displayed. The specimen is a 

 highly interesting one. The part above the elongate oval seed is 

 the style, or remanet of the pistil, and would probably furnish a 

 capital subject for observation of the descent of the pollen-tubes. 

 The fruit is elevated on a long, slender stalk (PI. XIV., Fig. 7), 

 probably an elongate disc. The hairs at the base represent the 

 perianth ; they are about 36 in number, and may be considered 

 as composed of three whorls, of 12 in a whorl, equivalents of 

 petals, sepals, and bracts. The genus is closely related to the 

 Aracecz (type, Arwn maculatiim^ " Lords and Ladies "), and to the 

 Screw Pines. Every part contains abundance of prismatic 

 raphides. I should like to see fruit of the Lesser Bulrush {Typha 

 All gustif olid) ; the plant is of occasional occurrence throughout 



