ISAKIACEI. 



C 442 ] 



ISOETES. 



growth, bears the claviform receptacles of 

 Isaria ; and at a still later period, some of 

 the larvse hear the claviform receptacles and 



Fig. 375. 



Isaria citrina. A single plant, showing the fruit. 

 Magn. 20 diams. 



the conceptacles, containing asci, ofSphceria 

 miUtaris. The spores (or conidia) of the 

 Bofri/tis-form and of the Isaria-iovm. are 

 capable of germination. 



BiBL. Berk. Hook. Br. Fl. vi.pt. 2. 464; 

 Ami. N. U. i. 2o9, vi. 132, pi. 12. fig. 12, 

 1850, V. 464; Fries, Su7nma Veget. 464; 

 Moutagne, Ann. So. Nat. 2 s^r. v. pi. 12. 

 fig. 3 ; Tulasne, Ann. Sc. Nat. 4 ser. viii. 35. 



ISARIA'CEI.— A family of Hyphoniyce- 

 tous Fungi, growing on decaying animal 

 substances or larger Fungi, characterized 

 by a cellular receptacle formed of fila- 

 ments approximated together and conjoined 

 throughout their whole length, each fila- 

 ment terminating in a spore. Recent ob- 

 servations throw doubt on the independ- 

 ence of this family, which perhaps consists 

 simply of conidiiferous forms of other genera. 



British Genera. 



Isaria. Receptacle clavately branched, 

 formed of densely interwoven coalescent fila- 

 ments, or cellularly fleshy. Spores borne on 

 simple sporophores arising on all sides. 



Ant.hina. Receptacle clavately branched, 

 formed of parallel filaments, loosely inter- 

 woven or free, feathery or villous at the 

 summit only, where they form the simple 

 sporophores. 



Ceratium. Receptacle somewhat^ horn- 

 shaped, of a mucilaginous consistence, 

 sprinkled with filaments which are sur- 

 mounted by naked spores. 



I'SIAS. — A genus of Copepodous Ento- 

 mostraca. I. davijjes, in British seas. 

 (Brady, Copepoda, Bay Soc. i. 62.) 



ISINGLASS.— This material consists of 

 finely-divided shreads of the swimming- 

 bladder of species of Sturgeon, and con- 

 sequently exhibits structure under the mi- 

 croscope, consisting of a fibrous tissue with 

 here and there fragments of blood-vessels 

 &c. It is sophisticated with cut gelatine, 

 which is structureless and moreover becomes 

 more translucent when soaked in water, 

 while isinglass becomes opaque and white. 



BiBL. liassall, Adidterations, .309. 



ISOCniLI'NA, Jones.— An oblong equi- 

 valved Ostracode, belonging to the Leperdi- 

 tiadce, and found only in the Silurian rocks 

 of Canada, Russia, and Bohemia. 



BiBL. R. Jones, Ann. N. H. 3. i. 248; 

 Schmidt, Mem. Acad, St. Petersh. xxi. 2, 



ISOETES.— A genus of Psiloteee (Lyco- 

 podiacete). /. lacustris, Quillwort, the only 

 British species, occiu's in mountain-lakes. 

 Isoetes is very remarkable in its mode of 



growth. 



The woody substance of the stem, like 

 that of the Lycopodiacefe generally, is a 

 solid central body, without a pith ; it is 

 surrounded by a thick parenchymatous 

 rind, which makes up the greater part of 

 the mass of the corm ; the woodj^ mass itself 

 is cylindrical above, and somewhat hemi- 

 spherical below, the convexity downward, 

 and it has a layer of cambium not only over 

 the growing apex, but over the convexity 

 of the sides and lower surface. Every year 

 a new portion of wood is added to the 

 upper end, and also to the outer angle of 

 the convex lower mass. The roots are pro- 

 duced in cycles of tens, sometimes one, 

 sometimes two in a year ; in each cycle the 

 oldest root is the inmost ; but the succeed- 

 ing cycles appear in the middle of their 

 predecessors, and push them out, and up to 

 the side. The rind is renewed every year 

 by the cambium layer ; and tiie latter, in its 

 growth to increase the size of the corm, by 

 degrees covers up and encloses the remains 

 of the earlier roots (as the woody layers 

 of Dicotyledonous trees overgrow broken 

 branches, bury them, and convert them 

 into imbedded knots). The leaves are of 

 delicate organization, and contain four lon- 

 gitudinal air-canals, with septa at intervals, 

 and one vascular bundle ; they are expanded 

 at the base, and contain the immersed spo- 

 ranges. DeCandolle says the epidermis has 

 stomata. The sporanges are of two kinds, 

 or rather bear two kinds of spores ; and 

 there appears to be a periodicity in their 

 development. The fronds of I. lucmtris are 



