CIRCULATION IN PLANTS. 379 



was first discovered by Mr. Holland with his triplet micro- 

 scope in 1832. Th^ movement of the globules is the same, 

 but much more delicate than in the Tradescantia, the nucleus 

 also being present; a magnifying power of four hundred 

 diameters, at least, should be employed to examine this delicate 

 object ; it may be seen dry or in water between glasses. 



Vallisneria spiralis. — This plant is a native of various ps-rts 

 of the world, but in the south of Europe, the East Indies, and 

 America, it appears to grow most abundantly. The name 

 spiralis was given to it by Linnaeus, But in order to distin- 

 guish it from an Italian plant of the same genus, it has been 

 termed by Sprengel V. Jacquiniana. Its natural habitat is 

 the still portions of rivers and lakes, and for the beautiful 

 contrivance, displayed in the mechanism for keeping its 

 flowers above the water, it has been the theme of the poet's 

 song. When growing, its appearance is not at all inviting, as 

 it very much resembles so much grass in the water, the long 

 thin leaves being secured to the mud by numerous white hair- 

 like roots. But to compensate for its uninteresting appearance, 

 the phenomenon of the circulation disclosed by the microscope 

 is, without doubt, the grandest that has as yet been seen in the 

 whole vegetable kingdom. If one of the leaves be laid on a 

 glass slide, and a sharp knife passed along it with its back 

 slightly elevated, so that its edge may come in contact with 

 the leaf, a thin slice may be cut off; this, when placed under 

 a power of two hundred diameters, will exhibit a number of 

 oblong cells, more or less full of green granules, which, 

 generally speaking, will be found to be in continued circulation 

 round the walls of each cell. If the section should chiefly 

 consist of the outer part or cuticle of the leaf, the cells wiU be 

 small, and the green globules, termed chlorophylle, in the 

 greatest abundance, but rarely circulating; if the section 

 should extend through the middle of the plant, numerous elon- 

 gated colourless cells will then be seen with green particles 

 only present on the margins, and these in active circulation, 

 and accompanying them a large, more or less transparent, 

 nucleus ; the movement of the granules is more plainly seen 

 than in the Chara and Nitella, on account of the transparency 



