PARTS OF THE EMBRYO PLANT. 335 



from which a new plant is produced. Germination takes place in 

 any part of its surface, and not from fixed points. It sometimes 

 presents filaments or vibratUe cUia on its surface (figs. 467-470, p. 

 265), by means of which it moves about in fluids, like some of the 

 Infusoria. When it germinates, these cUia disappear. Sometimes 

 spores are united in definite numbers, as in fours, surrounded by a 

 cellular covering, or perispore {•rri^i, around, and a'Tto^a, offspring), or 

 sporidium, and thus forming the reproductive body called a tetraspore 

 (rsT^Ag, four), which is common in Algse (fig. 482, p. 273). 



Embryo. — In the embryo or corculum (corculum, a little heart), 

 the first part formed is the axis, having one of its extremities turned 

 towards the suspensor, and the other in the opposite direction ; the 

 former indicating the point whence the young root or radicle is to 

 proceed, and the latter that whence the leafy stem is to arise. The 

 part which produces the first leaves or cotyledons is called the cotyle- 

 donary extremity of the embryo, while the other is the radicular 

 extremity. The radicular extremity is thus continuous with the 

 suspensor, and consequently points towards the micropyle (fig. 590 h), 

 or the summit of the nucleus, an important fact in practical botany ; 

 while the cotyledonary, being opposite, is pointed towards the base of 

 the nucleus or the chalaza (fig. 590 c). Hence, by ascertaining the 

 position of the micropyle and chalaza, the two extremities of the. 

 embryo can in general be discovered. In some rare instances, in 

 ■consequence of a thickening in the coats of the seed, as in Eioinus 

 (fig. 579, p. 329), and some other Euphorbiacese, there is an alteration 

 in the micropyle, so that the radicle does not point directly to it. 



The part of the axis which unites the radicle and the cotyledon 

 or cotyledons is denominated caulicule or tigelle (figs. 595 i, 597 t). 

 This is sometimes very short. From the point where the cotyledons 

 are united to the axis a bud is developed (in the same way as from 

 the axil of leaves) ; this bud contains the rudiments of the true or 

 primordial [primus, first, and ordo, rank) leaves of the plant, and has 

 been called plumule or gemmule. This bud may be seen usually lying 

 within the cotyledons. Thus in fig. 597 

 the embryo of the Almond exhibits the 

 gemmule, g, lying on one of the cotyledons, 

 the other having been removed and leaving 

 a cicatrix, ic ; while in fig. 595 the gem- 

 mule, g, of Potamogeton perfoliatus is 

 covered by the single cotyledon, c. 



The gemmule as well as the cotyledon 

 are sometimes obscurely seen. Thus in ^z- 698. Kg. 599. 



Fig. 698. Spiral embryo of Cusouta or Dodder. Fig. 699. Embryo of Caryocar buty- 

 rosum. *, Thick tigelle or caulieule, forming nearly the whole mass, becoming narrowed 

 and curved at its extremity, and applied to the groove, s. In the figure this narrowed 

 portion is slightly separated from the groove, c, Two rudimentary cotyledons. 



