VALVULINA. 



[ 800 ] VASCULAR BUNDLES. 



of observing the ROTATION in the leaves. 

 This plant is dioecious ; and the specimens 

 ordinarily found in cultivation are the pistil- 

 late forms, which often produce flowers, 

 but the seeds, remaining unfertilized, never 

 ripen j the plant increases rapidly, however, 

 by runners, if in a healthy condition. We 

 find it thrive well in any situation indoors 

 near a window and not exposed to frost ; but 

 it attains a far larger size in water kept at a 

 high temperature, as in Fzetfona-tanks in 

 Botanic Gardens. It is necessary, when 

 STpwing it in jars, not to keep too many or 

 too large snails in the water, as they destroy 

 the leaves. See ROTATION. 



VALVULI'NA,D'Orb. A genus of Are- 

 naceous Foraminifera. 



Typically it has a triserial, three-sided, 

 pyramidal shell, with three chambers in a 

 turn of its spire and a valved or tongued 

 aperture. The trifacial compression disap- 

 pears in a common trochoid form, which 

 becomes scale-like and flat. If the cham- 

 bers fail to make a coil, an obliquely semi- 

 oval shell is produced, with a broad oblique 

 septal plane and a large valve, which bridges 

 over the crescentic aperture with bars. The 

 triangular form sometimes becomes Bulimi- 

 noid ; and often takes on a uniserial growth 

 (Clavulina, restricted), either cylindric, tri- 

 carinate, or five-angled. Numerous forms, 

 recent and fossil. V. austriaca (PI. 23. f. 20). 



BIBL. Parker & Jones, Ann. N. H. 3. v. 

 467 ; Carpenter, Foram. 146 j Brady, Carb. 

 For., Pal. Soc. 1876, 81. 



VAMPYREL'LA, Hckl. A doubtful 

 genus of Radiolarian Rhizopoda. Body 

 red, rounded, without nucleus or contractile 

 vesicle, and with very slender pseudopodia. 

 These animals perforate the cells of Spi- 

 rogyra and Gompkonema,&nd feed upon their 

 contents. In the encysted condition, they 

 are stated to possess an outer nitrogenous 

 and an inner cellulose coat. 



BIBL. Haeckel, Qu. Mic. Jn. 1869, 33 ; 

 Schnitzel Arch. 1876, xii. 24. 



VARIOLA'RIA,Pers. A spurious genus 

 of Lichens, founded upon imperfect forms 

 of PERTUSARIA &c. 



BIBL. Hook. Br. Fl. ii. pt. 1. 172 ; Schae- 

 rer, En. Grit. 229. 



VASCULAR BUNDLES. This title is 

 applied to the fibrous cords which form the 

 ribs, veins, &c. of the leaves, petioles and 

 other appendicular organs of all plants rank- 

 ing above the Mosses, and which by their 

 confluence and more considerable develop- 

 ment constitute the wood of stems and 



trunks. The vascular bundles of petioles 

 (fig. 660, page 711), &c., running into leaves 

 to form their ribs, and lying imbedded in 

 parenchyma, resemble the bundles which 

 form the rudiments of wood of the stem 

 itself. The bundlesremain isolated as fibrous 

 cords in the stemsof the herbaceous Monoco- 

 tyledons, or are only combined into a wood, 

 in the Palms &c., by the lignification of the 

 cells of the parenchyma in which they are 

 imbedded (fig. 461, p. 508). 



In the Dicotyledons, the rudimentary 

 bundles are developed in a circle surrounding 

 the pith (fig. 455, p. 495), and soon unite 

 to form a tube of wood, with an external 

 cambium layer and a true bark j and the 



Fig. 791. 



Monocotyledon. 



Transverse section of a nbro-vascular bundle of a 

 Palm : the upper end is directed towards the centre of 

 the stem, w, woody fibres resembling liber in struc- 

 ture ; s. v, spiral vessels ; c, cambium (vasa propria) ; 

 d, ducts ; p, parenchyma ; /, liber ; I. c, laticiferous 

 canals. Magnified 150 diameters. 



cambium layer is the seat of renewed de- 

 velopment of the vascular bundle in each 

 successive year. On such characters of 

 growth, Schleiden founded a division of the 

 vascular bundles into classes which are con- 

 venient in reference to microscopical inves- 

 tigations, and affixed tolerably perfect syste- 

 matic characters to them. 



In the higher flowerless Plants, viz. 

 Ferns, Equisetacese, &c., the vascular bun- 

 dles ate composed chiefly of ducts, sur- 



