84 NATURAL SCIENCE. August, 



Journal (vol. xxxi., pp. 312-363) comprises his monograph, or, as he 

 prefers to style it, " general view " of the genus Cupressns. Cypresses 

 are distinguished from their near allies the Thujas, v/hich have similar 

 foliage, by the shape of the cone-scales, those of the former having a 

 shield-shaped expansion at the free end, which is absent in the latter. 

 In Cupycsstis, also, each scale bears two or more seeds ; in Thuja 

 some scales only are fertile. 



There are fourteen species, which, however, are so variable that 

 it is hard to find distinctive characters which shall be generally 

 applicable, A further difficulty arises from the polymorphy of the 

 individual, the plant assuming different appearances at different 

 periods of its growth. These stages of growth are usually transitory, 

 but occasionally become more or less persistent, and when the whole 

 or greater part of the plant is concerned, may produce an appearance 

 quite different from the usual one. The "genus" Retinospova was 

 founded on such plants, now known to belong to species of Cypress, 

 Juniper, and Thuja. The identity is proved by the existence of inter- 

 mediate forms on the same tree, by the presence of cones characteristic 

 of the species, and by the fact that the leaf-characters of ^^Retinospova " 

 are also true of the seedling plant, which only gradually assumes the 

 adult foliage. 



An interesting physiological difference exists between the various 

 kinds of foliage. Cuttings bearing the primordial leaves strike freely, 

 while those bearing the adult form take root less readily, " as if the 

 vegetative energy were more or less arrested in anticipation of the 

 commencement of the reproductive stage." Occasionally, however, 

 flowers are borne on shoots bearing primordial leaves, as in a form ol 

 Cupressus pisifera, one of the Retinosporas. 



Another feature, one of important xiorticultural value, is the 

 tendency to " fastigiation," or an upward growth of the branches at 

 an acute angle, such as occurs also in the Irish Yew. 



Cypresses are found in a native state from South-eastern Europe, 

 through the Levant and Persia, to the Himalayas, and in China and 

 Japan. In the New World, there are two species in North-west 

 America, several in California and the mountains of Mexico, and 

 Guatemala; while on the eastern side of the Northern Continent 

 C. thyoides extends from north to south. 



Diatoms. 



There is evidently some work to be done on these microscopic 

 algae. At the Linnean Society's meeting on June i8th, Mr. G. Murray 

 shewed a series of lantern-slides, illustrating some very important 

 observations on their reproduction. Professor Cleve has already figured 

 in a Swedish journal a specimen of Biddnlpliia aiivita, showing a young 

 individual within the mother-cell. In the same genus Mr. Murray 

 has also observed a still earlier stage, showing the contraction and 



