38 BOTANY. • 



the reproductive organs of cryptogamous plants, and now propose to combine 

 these under one general head, with the addition of some points hitherto 

 omitted. In the case o Ferns, reproduction is efTected by means of sjW7'es, 

 inclosed in cases named thecce, which often form in clusters or sori on the 

 under side of the leaves, or beneath the epidermis. This latter, when includ- 

 ing the thecae, is called the bidnsimn. The thec£B, or spore cases, have 

 frequently a stalk passing up one side, and disappearing on the other ; the 

 point where this is attached is called the annuhis. 



Urn Mosses are increased by spores contained within an ?/?•??, placed 

 at the apex of a seta or stalk, bearing on the summit a loose hood, called a 

 calyptra, and closed by a lid or operculum. At the base of the spore case is 

 sometimes found a tumor or struma, or an equal expansion, termed apophysis. 

 The inside of the thecfe has a central axis, or colum,ella ; and the orifice 

 beneath the operculum is closed by teeth-like processes, or a membrane called 

 peristo?ne. 



Lichens are cellular expansions, consisting of a thallus, or combination 

 of stems and leaves, upon which appear shields or apothecia. These arc 

 the reproductive organs, and consist of a margin inclosing a kernel or 

 nucleus, in Avhich are imbedded tubes containing sporules, and termed 

 asci. 



In the highest forms of Fungals there are two kinds of organs : one, cys- 

 fidia, conical naked elevations ; the other, basidia, also conical elevations, but 

 bearing spores on their apex. 



GENERAL CONSIDERATIONS WITH RESPECT TO PLANTS. 

 A. The Chemical Constituents of Pl.4.nts. 



Plants are composed of certain chemical elements, Avhich are combined 

 in various ways, so as to form either organic or inorganic compounds. The 

 former are composed of carbon, oxygen, hydrogen, and nitrogen, with a 

 certain proportion of sulphur, or phosphorus ; the latter consist of various 

 metallic bases, combined with metalloids and acids. Water is a chief con- 

 stituent of plants, the amount being determinable with approximate accuracy, 

 by drying the plant at a heat slightly exceeding that of boiling water, and 

 estimating the loss of weight. When the plant is burned the organic con- 

 stituents «disappear, and the inorganic are left in the form of binary or ternary 

 compounds. 



Carbon is the most abundant constituent of the plant, forming a greater 

 proportion of its mass than any other. When vegetable matter is heated 

 without exposure to air, the carbon is left in the form of charcoal, of a black 

 color and porous texture, retaining much of the original volume and shape. 

 It exists in great quantity in the soil, but requires to be converted into 

 carbonic acid before it can be taken up by the plant. Most of the carbon 

 of the plant is derived from the decomposition of the carbonic acid of the 

 38 



