YALE AGRICULTURAL LECTURES. 21 



its form, size, structure, contents, origin, and mode of growth. 

 The vegetable cell, he says, is a closed vessel like an egg, and 

 is composed of an outer solid membrane which contains a fluid, 

 and matter floating in the fluid, or attached to the sides. At 

 first the enclosing membrane is very delicate, and is called a 

 utricle / if this remains closed throughout its life, it is called 

 " a cell ;" if the sides of several adjoining cells disappear, and 

 the series is arranged into a tube, it becomes "a vessel." Cells 

 are the base of all vegetation. The red snow-plant, and the 

 yeast-plant, are single cells. The snow-plant, so graphically 

 described by Kane and other Arctic explorers, is one cell, with 

 little particles floating within. These particles become cells 

 themselves, in time, and the outer coat bursting, lets them 

 escape to commence an individual existence themselves. Cells 

 vary in form in different plants, and even in the same plant 

 they, by overcrowding here and loosening there, get distorted 

 in shape. In the stems of water-lilies some of the cells are 

 star-shaped, while in the wood of trees they are long and pipe- 

 like. The diameter of cells averages from l-1200th of an inch, 

 up to 1 -250th ; but the common puff-ball of our pastures, when 

 broken, spirts out a fine brown powder, each particle of which 

 is a cell, or spore as it is termed, of infinitesimal diameter. 



The membranous wall of cells is of different toughness. In 

 the sea-weed, it is very soft ; in ash, hickory, and mahogany, 

 very hard ; and in vegetable ivory, harder still. Cell membrane 

 never dissolves in water, but swells. It is called " cellulose," 

 and is composed of oxygen, hydrogen, and nitrogen, chemically 

 written thus : C. 12 ; O. 10 ; H. 10. The spaces between the 

 cells of a plant are filled variously : sometimes with air ; in the 

 common red cedar, with minute grains of red aromatic rosin ; 

 in sumac, with a thick milky sap ; and in other plants, with 

 gums. The contents also of cells vary. The growing cells of 

 some plants, as asparagus, are more nutritious, because they 

 contain some nitrogen, which goes toward making muscle in 

 the animal body. A granular matter, a viscid fluid, sap (which 



