138 THE SEED. 
s 4 2 
the radicle is at the hilum or base of the seed, as in the Po- 
macee, the Solanew, &c. In this position it is sometimes 
called erect ; and the nucleus is inverted. 
542. The embryo is antitropous or inverted when the co- 
tyledons are next the hilum, as in the Thymelex, Urticee. 
In this case the radicle is remote from the hilum. 
543. The embryo is heterotropous when it lies across the 
hilum, as in Primulacez. 
544. The embryo is amphitropous when carried round the 
albumen, so that the two extremities approach, as in the Ca- 
__ ryophyliez. 
545. There is a peculiar class of plants which are con- 
stantly destitute of floral envelope, sexual organs, and seeds. 
They are reproduced by means of minute bodies, called spo- 
rules, which, indeed, may be considered as the seeds, but beat 
no analogy in mode of formation or in structure to the seeds 
which have just been examined. 
546. The sporules of flowerless plants are of a homoge 
neous structure, not separable into gemmule, radicle, and co- 
tyledons ; and capable of germinating from any point. In 
monocotyledonous and dicotyledonous plants, the process of 
germination proceeds upwards (into stem) and downwards 
_ Gnto root) from one particular point—the neck. But in the 
flowerless plants, the root and stem seem to be capable of 
proceeding indifferently from any part of the sporule. = 
547. They are called Acotyledonous, from being destitute 
of cotyledons ; Inembryonate, from being destitute of an e™ 
bryo; Asexual, Agamic, and Cryptogamic, because they ha 
no sexual organs, or because, if these do exist, they cannot 
be detected: and Cellular, because they are found to 
_ chiefly of cellular tissue, or are destitute of spiral vessels. E 
648. These differ in many other respects from phenogami¢ 
or flowering plants; and consist chiefly of the following 
tribes: Ferns, (Filices), Mosses (Musci), Mushrooms (Fu 
‘gd. Sca-Weeds (Alga). ‘The General Anatomy of thee 
