cave, with two spurs or pouches at the base 

 instead of one, and in the capsule, which is 

 not flat ; while from Hemimeris they are 

 chiefly distinguished by their four sta- 

 mens, all usually bearing anthers, the fila- 

 ments of the lower ones curved round at 

 the base so as to embrace the upper ones. 

 There are about twenty species known. 



DIASPASIS. A genus of Goodeniacece, 

 containing a single species, B.filifolia, a 

 native of the south-west coast of Australia. 

 This has an adnate calyx with five short 

 teeth, a nearly regular salver-shaped rose- 

 coloured corolla with a five-parted limb, 

 and free included stamens. The peduncles 

 are axillary and single-flowered ; the leaves 

 alternate and nearly terete. [R. H.] 



D1ASTEMELL A. A genus of Gesneracece, 

 containing a single species from Costa 

 Rica. It is a slender hairy herbaceous 

 plant, with ovate serrate and petiolate 

 leaves, and flowers in axillary racemes. 

 The corolla is slightly oblique and ringent, 

 and the limb bilabiate, with the upper lip 

 I two-lobed, and the lower one trifld. The 

 four stamens are included, and with the 

 rudimentary fifth are inserted on the base 

 of the corolla. The capsular fruit is mem- 

 branaceous. [W. C] ■ 

 DIASTEMMA. A genus of Gesneracece, 

 . containing thirteen species natives of 

 I South America. They are perennial sto- 

 lonif erous scaly herbs with opposite leaves, 

 and small flowers in axillary corymbs. 

 The calyx is adherent to the base of the 

 ovary ; the corolla is oblique, erect in the 

 calyx, with a tube subcylindrical or in- 

 creasing upwards, and a five-lobed spread- 

 ing limb ; the four stamens are included, 

 the fifth rudimentary ; the anthers are 

 small and coherent. The ovary is sur- 

 rounded by five elongate glands, and sur- 

 mounted by a bilamellatc stigma. [W. C] 



DIATOMACECE. A very distinct natu- 

 ral order of green-spored Algce, remarkable 

 for the enormous quantity of silex con- 

 tained in their frond, and for their yellow- 

 brown colour. The mode of increase so 

 closely resembles that of Desmidiacece, 

 that in this respect, we refer for informa- 

 tion to that article. Their claims to a place 

 amongst animals was even more strongly 

 contested than in that order, but Mr. 

 Ralf s' discovery of the formation of spores 

 byconjugation inseveral genera has effectu- 

 ally put an end to controversy. The spe- 

 cies are often attached by a slender pedun- 

 cle when young, and in some genera this is 

 repeatedly dichotomous. The joints often 

 remain connected for a long time, separa- 

 ting in some instances alternately above 

 and below so as to form a curious chain. 

 When connected they form various shaped 

 fronds, as linear, flabelliform, circular, &c. ; 

 but in a multitude of instances disarticu- 

 lation takes place with the formation of 

 each new individual. The separate joints 

 which have received the name of frustules 

 exhibit frequently a totally different out- 

 line when seen dorsally and laterally, and 

 they are almost always adorned with deli- 



cate streaks and other markings. In Cosci- 

 nodiscus they form a disk with circular 

 apertures like a colander. In many cases 

 the frustules have distinct external aper- 

 tures in the siliceous coat, without which 

 it is not easy to see how there could have 

 been a proper communication with the 

 surrounding medium from which they 

 must derive their nourishment. In conse- 

 quence of the large proportion of silex 

 which they contain, the frustules are 

 capable of retaining their form after all 

 vegetable constituents have fled, and thus 

 they are admirably adapted for preservation 

 in a fossil state. Vast beds accordingly' 

 occur, many feet in thickness, consisting 

 entirely of effete frustules. known under 

 the name of Tripoli, and affording an ad- 

 mirable material for polishing, for which 

 they are used extensively. ' The phonolite 

 stones of the Rhine,' says Dr. Hooker, ' and 

 the Tripoli stones, contain species identical 

 with what are now contributing to form a 

 sedimentary deposit, and perhaps at some 

 future period a bed of rock extending in 

 one continuous stratum for 400 measured 

 miles. I allude to the shores of the 

 Victoria barrier, along whose coasts 

 the soundings examined were invariably 

 charged with diatomaceous remains con- 

 stituting a bank which stretches 200 miles 

 north from the base of the Victoria bar- 

 rier, while the average depth of water 

 above it is 300 fathoms or 1800 feet. 

 Vast quantities again occur in bed under 

 the guise of a white powder, which is 

 called mountain meal, and is actually 

 mixed with flour in some parts of Swe- 

 I den, though it is perfectly inert, and can 

 | serve merely to increase the bulk of the 

 food, a circumstance of some importance 

 ' where it is scarce.* The walls of the 

 frustules are so thin, and the little cells 

 of silex so light, that they are often wafted 

 to great distances by the trade and other 

 winds, so that species of remote regions 

 may occasionally occur in a dead state in 

 countries where they could not maintain 

 \ their existence. Diatomacece form a large 

 I portion of the food of some of the lower 

 | moOusks, which in turn are preyed on by 

 1 sea birds ; and as the shells are capable of 

 ! resisting digestion, they are found, fre- 

 quently in great quantities, in the beds of 

 ; manure which are collected for agricultural 

 j purposes under the name of guano. Many 

 I unique species have been obtained by 

 travellers from the stomachs of fish, which 

 I sometimes afford an abundant harvest for 

 I the microscope. Diatomacece occur in all 

 , parts of the world, and abound amongst 

 the ice and in the deep sea of polar regions. 

 They probably are the plants above all 

 others capable of enduring extreme de- 

 grees of cold without annihilation ; while, 

 on the contrary, several occur in springs of 

 high temperature. The striae on the walls 



* Experiments in cattle-feeding show that the 

 relative quantity of nutritious matter in food, in- 

 dependent of the bulk, is not the only point worthy 

 of observation. The stomach must be properly 

 filled, or, as it is termed in French, leste, or the 

 due effect of the nutriment -will not be obtained. 



