12 



DIATOMACE.E. 



[Algals. 



Order I. DIATOMACEiE. Brittleworts. 



8. 529 ; Part of Chaodinese and Fra- 

 Gen. I. ; Ralfs. in Ann. Nat. Hist. 



Diatomacese, Agardh, Syst. xii. (1824) ; Kutzing, in Linnaa, 

 gillarise, Boi-tj in Diet. Class. Z. and 4. (1823) ; Endltch. 

 11 et scq. 

 Di.\G^osis.— Crystalline, ang^dar, fragmentary bodies, brittle, and midtiplying by 



spontaneous separation. 

 Cnstalline fragmentary bodies, generally bounded by right lines, rarely included in 

 curved lines, flat, stiff", brittle, usually nestling in slime, uniting into various forms, and 

 then separating again. 



Those who have ever examined the sm-face of stones constantly moistened by water, 

 the class of hothouses, the face of rocks in the sea, or of walls where the smi never shmes, 

 or the hard paths in damp parts of gardens aft;er rain, cannot fail to have remarked a 

 green mucous shme with which such places are covered. This shme consists of Algals 

 in then* simplest state of organisation ; they have been called Chaodineae by Bory de 

 St. Vmcent, whose accomit of them is to the foUowmg effect : " The shme resembles a 

 layer of albumen spread \\ith a brush ; it exfohates in drying, and finally becomes 

 visible by the manner in which it colours green or deep brown. One might call it a 

 proAisional creation waitmg to be organised, and then assummg different fonns, accord- 

 ing to the natm-e of the corpuscles which penetrate it or develop among it. It may 

 further be said to be the origin of two very distinct existences, the one certainly animal, 

 the other purely vegetable. This matter lying among amorphous mucus consists, in 

 its sunplest state, of sohtary, spherical corpuscles ; these corpuscles are afterwards 

 grouped, agglomerated, or chained together, so producing more complex states of 

 organisation. Sometimes the mucus, which acts as the basis or matrix of the corpuscles, 

 when it is found in water, wliich is the most favom-able medium for its development, 

 lengthens, thickens, and finally forms masses of some inches extent, which float and 

 fix themselves to aquatic plants. These masses are at first hke the spawn of fish, but 

 they soon change colour, and become green, in consequence of the formation of interior 

 vegetable corpuscles. Often, however, they assume a milky or ferruginous appearance ; 



and if in this state they are examined 



imder a microscope, they will be fomid 



completely fiUed with the animalcules 



called Na^'iculari£e, Lmiuhnse, and Sty- 



larise, assembled m such dense crowds 



as to be incapable of swimming. In 



this state the animalcules are inert. 



Are they developed here, or have they 



found theu' way to such a nidus, and have they 



hindered the development of the green corpuscles ? 



Is the mucus in which they he the same to them 



as the albuminous substance in which the eggs of 



many aquatic animals are deposited ? At present 



we have no means of answering these questions." 



These form, no doubt, the extreme hmits of the 

 Vegetable and Animal Kingdom. Their regnlar 

 form, and the power of separating into distinct 

 particles, which the most of them have, are almost 

 as much the attributes of the mineral, as of the 

 vegetable, or even animal kingdom. Agardh in- 

 cludes them among plants. Kiitzing asserts that 

 then' life is as much animal as vegetable ; and that, 

 at all events, Achnanthes, Gomphonema, Exilaria, Fragila- 

 ria, Meloseu-a, Schizonema, Micromega, and Berkleya, are 

 at least plants, if Frustulia, C}-mbella, NaA-icula, Suru'ella, 

 (Sec, are animalcules. He has also recently ascertained, that 

 the frustides of jNJicromega are metamorphosed mto green 

 globular spores. Dr. Dickie of Aberdeen has observed some- 



Fig. II. 

 thing of the same kind. 



Mr. Ralfs, who has paid great attention to the history of these 



Fig. 11.— 1. Biddulpliia ; 2. Grammoneuia ; 3. Eunotia ; 4. Achnanthes ; 5. Amphitetras ; 6. Gloionema, 

 a production once referred to this order, but determined by Mr. Berkeley to be the eggs of an insect. 



