313 BOTANY. 



globular masses, which lie in the parenchyma just beneath 

 the epidermis ; these are composed at the bottom of an hyme- 

 nium-like layer of sterigmata (shown in Fig. 316, A and /, as 

 a layer of elongated cells). Each gterigma produces a chain 

 of cells, which are at first many-sided from mutual pressure, 

 but afterward spherical. By their gi-ovvth these globular 

 masses finally burst through the epidermis (Fig. 316, I., p), 

 and soon afterward, by the rupture of the thin investing 

 layer of cells (peridiuni), they become opened and cup- 

 shaped (Fig. 316, /., a, a, a). The now rounded cells are set 

 free as large yellow conidia (or secidiospores). At one time 

 this stage was supposed to constitute a distinct plant, and it 

 received the generic name of ^cidium, hence it is stiU 

 known as the secidium stage. 



In many (if not all) cases there is a second kind of repro- 

 ductive organ present, resembling in some respects the secid- 

 ium fruits Just described. These are smaller flask-shaped 

 cavities, which are filled with slender hair-like filaments (Fig. 

 316, Z, sp, sp) ; these are the spermagonia, and they pro- 

 duce, by the breaking up of the filaments, numerous ex- 

 ceedingly small oblong bodies, the spermatia. The function 

 of these is not known ; at one time it was supposed that they 

 were the male reproductive bodies, but it is very doubtful 

 whether they are of this nature. 



405. — The conidia (aecidiospores), when they fall upon the 

 leaves of the proper host plant, germinate, and penetrate 

 thestomata, thus reaching the leaf parenchyma, where a dense 

 mycelium is formed. Upon this are formed, within a short 

 time, stalked spores (uredospores. Fig. 316, ///., ur) ; these 

 finally burst through the epidermis, and form orange-colored 

 spots upon the leaves. The uredospores fall off very easily, 

 and germinate quickly, giving rise immediately to another 

 mycelium (Fig. 317, D), which produces uredospores, which 

 may, in turn, give rise to new mycelium, and so on indefi- 

 nitely. The function of the uredospores is clearly the quick 

 reproduction of the fungus. 



406. — After the production of uredospores has continued 

 for some time, the same mycelium gives rise to stalked, thick- 



