314 PART IV. VEGETABLE TAXONOMY. 



internal cell-formation, in certain large cells usually the terminal 

 ones of hyphae. The spores are usually eight in number, but in 

 some species there are but two and, in others four or five. They 

 have a thick outer wall and a thin extensible inner one. When 

 placed under conditions favorable for germination, the outer wall 

 bursts and the inner extends to form one or more tubes, from 

 which the hyphae develop. 



Usually the asci are produced in a specially developed organ 

 or sporocarp, which is often a complex structure constituting the 

 most conspicuous part of the plant ; but in a few forms the asci 

 are isolated, and not borne in a special fruiting-organ ; and in 

 other cases the latter is present, but has the simplest possible 

 structure. Normally, the production of a sporocarp and asco- 

 spores, is the result of an antecedent sexual process analogous 

 to that which occurs in most Phycomycetes, but this is not always 

 the case ; in a large number of instances the organs of sexual 

 reproduction either exist only in a rudimentary condition, or have 

 entirely disappeared. 



When sexual reproduction occurs, it takes place by means 

 of an archicarp and an antheridium, the former corresponding 

 to the oogonium of the Peronosporeae, but differing from it in 

 the fact that no oospores are developed within it, as well as in 

 the fact that the collateral growths resulting from fertilization 

 are usually very different. 



In some of the simpler species, the end of a hyphal branch 

 becomes enlarged and ellipsoidal in form, and is separated from 

 the rest by a septum to form the archicarp, and an adjacent 

 branch becomes less thickened, has its apical portion separated 

 from the rest by a septum in a similar manner, and becomes an 

 antheridium. In most cases, however, the filament that forms 

 the archicarp becomes twisted into a spiral, and covered perhaps 

 by an out-growth of adjacent hyphae to form a compact mass. 

 This may be provided with a projecting filament, or trichogyne, 

 which receives the fertilizing influence, or it may be without it. 



In the species which do not produce a trichogyne, the anther- 

 idium becomes entangled with the coiled filaments of the archi- 

 carp, and thus fertilizes them ; in the species that do produce 

 one, the antheridium, when ripe, discharges spermatid, small 

 fertilizing cells without cilia, which, by adhering to the tricho- 

 gyne, fertilize the archicarp. 



