ISARIACEI. 



[ 368 ] 



ISOETES. 



insects, fungi or twigs or leaves of plants. 

 J. farinosa, Fries, grows to a height of 

 1 2" on dead pupae, spiders' nests, &c. 

 I. arachnophila, Ditton, intricate/, r.,pube- 

 rula, Berk., and Friesii, Montagne, are also 

 British. I. citrina (figs. 378, 379) is a small 

 species, growing gregariously on vegetable 

 substances. 



BIBL. Berk. Hook. Br. Fl. vi. pt. 2. p.464; 

 Ann. Nat. Hist. i. p. 259, vi. p. 132. pi. 12. 

 fig. 12. 2nd ser. v. p. 464 ; Fries, Summa 

 Veget. p. 464 ; Montagne, Ann. des Sc. not. 

 2 se'r. v. pi. 12. fig. 3. 



ISARIACEI. A family of Hyphomyce- 

 tous Fungi, growing on decaying animal 

 substances or larger Fungi, characterized by 

 a cellular receptacle formed of filaments ap- 

 proximated together and conjoined through- 

 out their whole length, each filament termi- 

 nating in a spore. 



Synopsis of British Genera. 



I. ISARIA. Receptacle clavately branched, 

 formed of densely interwoven coale scent 

 filaments, or cellularly-fleshy. Spores borne 

 on simple sporophores arising on all sides. 



II. ANTHINA. Receptacle clavately 

 branched, formed of parallel filaments, loose- 

 ly interwoven or free, feathery or villous at 

 the summit only, where they form the simple 

 sporophores. 



III. CERATIUM. Receptacle somewhat 

 horn-shaped, of a mucilaginous consistence, 

 sprinkled with filaments which collapse into 

 minute granules (conidia) and free sporidia. 



BIBL. See the Genera. 



ISOETES. A genus of Psiloteae (Lyco- 

 podiaceae), consisting of plants, usually of 

 small size, growing at the bottoms of pools, 

 or in wet places. I. lacustris, the only 

 British species, occurs in mountain lakes. 

 Isoetes is very remarkable in its mode of 

 growth ; it is the only known plant possess- 

 ing a stem which never branches, moreover 

 the solid cone which supports the leaves 

 possesses a kind of cambium layer, from 

 which are produced successive layers of 

 woody structure, comparable in some mea- 

 sure with those of the Dicotyledons; besides 

 this, it has a striking peculiarity in the mode 

 of development of the (adventitious) roots, 

 the youngest of which are the lowest, the 

 older being gradually pushed upwards and 

 outwards towards the circumference. 



The woody substance of the stem of Iso- 

 etes, like that of Lycopodiacese 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 woody mass itself is cylindri- 

 cal above and somewhat semilunar 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 produced in cycles of tens, some- 

 times one, sometimes two in a year ; in each 

 cycle the oldest root is the inmost ; but the 

 succeeding 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 the latter in 

 its growth to increase the size of the corm, 

 by degrees covers up and encloses the re- 

 mains 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 longitudinal 

 air-canals, with septa at intervals, and one 

 vascular bundle ; they are expanded at the 

 base, and contain the immersed sporanges. 

 DeCandolle says the epidermis has stomates; 

 this appears doubtful. 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. la- 

 custris are discoverable in the interior of the 

 bud twelve months before they become fully 

 developed; the sterile originate in spring and 

 the earlier part of the summer, the fertile in 

 the autumn, while stunted fertile leaves ap- 

 pear even in the winter. If a vigorous leafy 

 plant is examined, it will be found to have a 

 few sterile leaves outside, then a circle of 

 leaves with oosporanges, next a circle of 

 anthero-sporanges, and in the centre of 

 the bud sterile leaves closing the annual cycle. 

 The sporanges are somewhat plano-convex, 

 longish-oval cases, with transverse processes 

 forming imperfect septa, dividing them into 

 several chambers (fig. 382). The cases are 

 sheathed by a membranous expansion of the 

 base of the leaf (fig. 381), to which they are 

 adherent by the back (fig. 382) ; the septa 

 arise opposite the point of attachment at the 

 back, and spreading out, join the front wall. 

 The different contents of the sporanges are 

 evident before they open, those with the 

 small spores having a smooth face, those 

 with large spores being rendered tubercular 

 from the protrusion of the wall by the under- 

 lying bodies. The wall of the capsule is 



