VILLI. 



[ 677 ] 



VINE FUNGUS. 



Fig. 808. 







Fig. 809. 



Fig. 808. Two villi from a calf without epithelium, and 

 containing each a lacteal vessel ; after treatment with 

 dilute solution of soda. Magnified 350 diameters. 



Fig. 809. Two contracted villi, from a cat. Magnified 

 6o diameters. 



When acteduponby water, the cell-membrane 

 at the snrface is separated, leaving a clearspace 



between the granular cell-contents and the 

 former. 



BiBL. Kolliker, Mikrosk. Anat. ii. 



VINCA, L. — The generic name of the 

 garden plants called Periwinkles; interest- 

 ing to microscopists on account of the stri- 

 ated liber-fibres (PI. 39. fig. 30). (See 

 Spiral Structures, p. 594.) 



VINE FUNGUS. — The vine mildew, 

 Oidium Tuckeri, Berk., which has in recent 

 years caused such extensive destruction, has 

 formed a subject of investigation for most of 

 the principal mycologists ; and notwithstand- 

 ing that its natural history is not yet wholly 

 cleared up, many interesting points have 

 been discovered. As it ordinarily appears, 

 it forms a white and very delicate cottony 

 layer upon the leaves, young shoots, and 

 fruits of the vine, soon causing a production 

 of brown spots upon the green structures, 

 and subsequently a hardening and a destruc- 

 tion of the vitality of the surface. Under 

 the microscope, the white substance is seen 

 to be composed of delicate ramified fila- 

 ments, creeping horizontally over the sm*face, 

 and w^hen the plant is much developed, form- 

 ing a dense interlacement. The horizontal 

 filaments exhibit few septa, these occurring 

 at the points of branching, and they do not 

 penetrate into the interior of the epidermal 

 layer; here and there, however, they are 

 found fixed to the epidermis by a more or 

 less developed organ of attachment, consist- 

 ing of a disk or lobed expansion (comparable 

 roughly to the so-called " root " of some of 

 the Fucoid Algae), which adheres firmly to 

 the cuticle, and when removed, leaves a 

 brownish scar behind. The destructive efi'ect 

 of the Fungus seems to arise from its arrest- 

 ing the development of the epidermis, by 

 binding its structures together, and excluding 

 the surface from the influence of the air, 

 since when young berries are invaded, the 

 internal development proceeds, and the 

 sphacelated epidermis preventing the natural 

 expansion, the grapes burst and rot. [In 

 this case, species of Botrytis, &c. appear 

 upon the decomposing pulp, as on all similar 

 substances; and these must be distinguished 

 from the proper mildew.] When full-grown 

 leaves are aifected to a moderate extent, the 

 vitality is often only partially affected, causing 

 a laxity of the tissue, and more or less 

 fading of the green colour, without inevi- 

 table decay. 



When the mildew is observed with a low 

 magnifier, its surface exhibits a mealy ap- 

 pearance, arising from minute bead-like or 



