398 



BOTANY OF THE LIVING PLANT 



Like other Thallophyta, Fungi may bear organs of sex, which lead 

 up to the production of accessory spores with attendant reduction 

 division. They thus show a life-cycle with successive phases com- 

 parable with that of autophytic plants. But in many of these which 

 are regarded as the most advanced, and especially in the larger 

 Agarics, sexual propagation is not normally carried out and the organs 

 of sex may be actually absent. Various stages of functional per- 

 version, and of atrophy of the sexual organs, are illustrated by less 

 advanced Fungi. Most Fungi have thus two forms of propagative 

 organs in their life-history : conidia, which are minute bud-like bodies 

 easily detached from the parent, which they produce vegetatively ; 



Fig. 296. 



Development and fertilisation of the ovum of Pythium. The granular protoplasm 

 of the oogonium (c) collects into a ball, and the antheridium sends in a fertilising 

 tube. In (b) and (c) transmission of contents into the ovum is shown, (d) The 

 ovum has formed a cell-wall, and lies loosely in the oogonium. Highly magnified. 

 (After Marshall Ward.) 



and spores (p. 401), which are formed as a consequence of a sexual 

 process, or take the same place in the life-cycle in those cases where 

 sexuality is absent. Some Fungi have more than two modes of propa- 

 gation. The propagative bodies may differ in appearance, though 

 they are really mere stages in one life-history : for instance, conidio- 

 phores and spore-fruits. Sometimes in parasitic Fungi these stages 

 may appear on different hosts, as in the Rust of Wheat, where the one 

 stage is on the Wheat, another on the Barberry (p. 432). Natur- 

 ally, before the facts were fully known, such stages were liable to 

 be regarded as different Fungi, and described by distinct names. 

 For instance, the Rust on Wheat was called Puccinia, while the 

 stage on the Barberry was described as Aecidium. Later these 

 were proved to be merely parts of the same life-history, and they 

 were given a single designation. But in many Fungi the life-h?story 



