THALLOPHYTES. 9 



cell is parted off from its upper extremity. The archicarp answers therefore to 

 the oogonium of the Peronosporeae, and yet is not an oogonium, for its protoplasm 

 does not contract to form an oosphere but the asci grow out from it, or, as in this 

 which is the simplest case, the archicarp -cell itself becomes the ascus (Fig. 6, E, cs\ 

 which is borne on a short cell forming the stalk. Branches arise from beneath the 

 stalk and form the envelope of the sporocarp h. 



The processes are somewhat more complicated in the case of Ascobolus, another 

 of the Ascomycetes. In Fig. 6, F, which shows a diagrammatic section of the sporo- 

 carp, w is the archicarp consisting of several cells, m a tubular branching anthe- 

 ridial twig closely applied to the archicarp. Numerous filaments then arise from a 

 central cell of the carpogone, which form asci at the upper end of their branches and 

 a number of spores in the asci. The envelope of the sporocarp, which is in this case of 

 considerable thickness, consists of filaments which spring from beneath the archicarp, 

 and form ultimately a compact false parenchyma enclosing the archicarp with the 

 ascogenous filaments which have sprung from it and the asci themselves. The 

 mycelium which produces the archicarps in the two organisms which we have been 



FIG. 6. Formation of a sporocarp in two Ascomycetes diagrammatically represented. Podosphaera, F Ascobolits 

 (after De Bary and Janczewski), TV archicarp, -m antheridial branch, cs asci, h envelope of sporocarp. 



describing, is insignificant in comparison with the large sporocarp which is produced 

 from the archicarp, and which continues to grow for a considerable time, in many 

 cases even when separated from the mycelium. 



The resemblance between the fertilisation of archicarps and of procarps is shown 

 also by the fact that there are Ascomycetes (see under Lichens) which like the 

 Florideae have a procarp with a carpogone and trichogyne, and in which spermatia 

 form a sexual union with the trichogyne, exactly as in the Florideae. 



To sum up briefly what has now been said with respect to the sexual process, 

 it may be stated that its result is always the formation of one or more spores, and 

 that the spores are either an immediate product of fertilisation, as the zygospores of 

 the Conjugatae, or they are the result of a vegetative process set up by the fertilisation, 

 as in the Ascomycetes, Florideae, &c. In extreme cases the product of fertilisation 

 is a definite mass of tissue which produces spores and in many Ascomycetes, for 

 example, is self-supporting, and thus appears as a special spore-producing generation 

 in contradistinction to the thallus, the sexual generation which bears the sexual 

 organs, a relation the meaning and value of which must be examined more closely 

 when we are considering the sharply defined alternation of generations in the 

 Muscineae and Vascular Cryptogams. 



