222 



HARDWICKE'S S CIEN CE-G OSS IP. 



STRANGE HABITATS OF CERTAIN 

 SPECIES OF DIATOMACEiE. 



fTlHE ubiquity of the lower forms of life, both 

 -*- vegetable and auimal, constantly attracts the 

 attention of the natural-history student. The only 

 preventive to the production and growth of organized 

 forms appears to be the absence of moisture. In 

 the boiling springs of Iceland, and in the snow of 

 the Arctic region, may be found microscopic 

 evidences of life. Nay, even in the acrid brine-pans 

 of Cheshire these simple forms "live, move, and 

 have their being." 



The Diatomaceas, like other low forms of life, 

 are almost invariably present wherever moisture 

 occurs, as among the roots of mosses growing in 

 humid situations, or among the confervoid growths 

 so^frequently seen on stones or walls exposed to 



Pn 



^2) 



Fig. 133. Ziparngpra denfrnteres : a, arcuate frustule ; b, 

 straight filament ; c, valve. 



spray from a fountain or the drip of a gutter. 

 Among the roots of mosses many species of Diatoms 

 seem to luxuriate, and one of the most remarkable 

 is Liparogyra dentroteres, Ehr. ; Orthosira mirabilis, 

 Gregory (" Trans. Mic. Soc," vol. iv. p. 37). Frus- 

 tules with spiral baud, vitreous, sometimes slightly 

 bent ; valve discoid, with three or more obscure 

 central puncta; margin set with short spines. (Wash- 

 ings from moss growing on alders, Heigham,Norfolkj 

 F. K. ; in moss from roof of cottage, Penzance, Ralfs ; 

 trunks of trees, Venezuela, Ehienberg. Fig. 133: a, 

 arcuate frustule ; b, straight filament; c, valve.) 



Ebrenberg describes two other species of the 

 genus ; viz., L. circularis, which seems to differ only 

 from the preceding in the greater number of lines 

 in the spiral (both forms were found in the 

 Venezuela gathering), and L. sea /art^, figured in the 



whichjt occurred in its original habitat, nor have I 

 seen the sporangial (?) state of it in gatherings from 

 other sources. 



Ortlio&ira D/c/l-?!?//.— Frustules straight, cavities 

 subspherical, valve discoid. Sporangial (?) frustule 

 fusiform, with undulate margin (Cave near Aberdeen, 

 Dr. Dickie; moss washings, Norfolk, F. Kitton. Fig, 

 135 : a, sporangial frustule ; b, ordinary frustules). 



Fig. 135. Orthosira Dichitii. 



Much obscurity exists as to the nature of the so-called 

 sporangial frustule. Mr. Thwaites, in his description 

 of this form ("Annals of Natural History," vol. i. 

 pi. 12, 2iid series), seems to have no doubt of its 

 sporanjiial nature. He thus describes its forma- 

 tion:-" At its commencement tlie endoclirome,at the 

 same time it withdraws from the end of the frustule, 

 produces at its centre an additional ring of cell- 

 membrane, and this process continues at certain 

 intervals. The author of the ' Synopsis of British 

 Diatomacese,' however, does not admit that it is a 

 sporangial condition of the frustule, but considers it 

 rather an abnormal development, analogous to 

 what sometimes takes place in other genera. In 

 no other members of this genus has there been found 

 any analogous process in the formation of sporangia. 

 Another difiiculty arises from the mode in which 

 self-division takes place in the sporangium, subse- 

 quent to its formation. It will be seen that after 

 the formation of a number of concentric rings of 

 silex, the sporangia assume an elongated fusiform 

 shape, and upon the cessation of this ring develop- 

 ment, an ordinary frustule makes its appearance, 

 occupying the central portion of the fusiform body, 

 but leaving the attenuated extremities unemployed. 

 Nitzschia i?/i;^/:r.— Frustule linear, valve linear, 

 lanceolate, arcuate, apices produced, strise distinct, 

 20 to 25 in '001". (Moss, Alder Carr, Heigham, 

 Norfolk,-fig. 13G.) 



^MM. 



Fig. 134. Liparogyra scalaris. 



Mikrogeologie, and which I have reproduced, fig. 134 

 (South America). In moss taken from very wet 

 localities I have occasionally found that very 

 remarkable filamentous diatom Orthosira Dickieii. 

 It does not occur in anything like the abundance in 



Fig. 136. Nitzschia viva*. 



I had formerly doubts as to the identity of the 

 moss form with the species usually found in brackish 

 water, but a careful compnrisou has sati.-fied me that 

 they are alike. On neither forms are the striae so 

 close as stated by Smith (30 iu '001"). 



