have often remained relatively obscure because they have simply been dismissed as asexual spores.But although mitotically formed, they are not 'a-sexual' since not only can they fuse with monokaryotic hyphae of their own taxon, but some also produce growth substance(s)which attract the hyphae of their own or closely related taxa. Thus a spermatium can be "recognized' by the hyphal tips of a growing colony of the same or similar species: Kemp (pers. comm.) has claimed that the "homing response'', as he calls it, is not species-specific, and can occur between a hypha and an arthroconidium of closely related species. This homing reaction can frequently be observed within 1-2 hours.Homing is a very valuable tool for the taxonomic agaricologist, because the response is often found in closely related species, and although a lethal reaction may follow, at least by this means one can ascertain the relative closeness of two taxa.Ecologically, the arthroconidia probably act as 'sterilizing' agents in any microhabitat, suppressing the growth and establishment of any late-comers, or restricting them to other ecological niches.Undoubtedly there is a stimulatory series in the genus Coprinus (Coprinaceae), for although there are two basic types of arthroconidium, 'wet' and 'dry', the former are frequently poor at germinating although strong attractors, whilst the latter germinate freely but are not usually good at causing the 'homing' effect. Dry and wet conidia are uncommonly found together in a single species.A range of conidiophores is produced within a single genus such as Coprinus (Fig. 19.1A §& H), and, by screening as many species as possible, work in Edinburgh has shown that the kind of branching of the conidiophore often reflects the infra-generic grouping. Thus Kemp (pers. comm.) has shown that, in the two species of Subsect. Comqtt he studied, spherical arthroconidia are formed on candelabra-like conidiophores, but those in Subsect. Lanatult form arthroconidia which coalesce into small 'wet' heads held above the vegetative mycelium.In the Sect. Hemerobit (s.g. Pseudocoprinus Kithner emend. Orton § Watling, ined,) the variation in conidiophore morphology is much greater, in my opinion reflecting the greater diversity of the genus, a diversity which is also seen in the range of mating patterns exhibited, i.e., homothallic, 2-spored or 4-spored, bipolar or tetrapolar, and vegetative hyphae with or without clamp-connections. In 2-spored C. sassit M. Lge & A.H. Smith, and 4-spored C. hiascens (Fr.) Quél., short conidiophores are formed, reduced still further in C. congregatus (Bull. ex St. Amans) Fr., where the arthroconidia are formed in tufts more or less directly on the vegetative hyphae. Species forming wet or dry arthroconidia are found in the Setulosi, and in some species conidiophores are absent altogether. C. pellucidus Karst. and C. steZlatus Buller are both homothallic, lack clamp-connections and form dry conidia; in contrast, wet conidia are formed in C. congregatus. The wet arthroconidia apparently possess a s...