84 FIRST GROUP. — THALLOPHYTES. 



another, which, if it runs its full course, ultimately produces zygospores or oospores, 

 having in most cases previously given birth asexually to brood-cells (gonidia, 

 zoogonidia). From the germinating spore a new thallus is developed either direcdy 

 or indirectly through a previous formation of gonidia (or zoogonidia), a variation 

 which may depend sometimes on outward circumstances. These Fungi, viz. the 

 Zygomycetes, Peronosporeae, and Saprolegnieae, are named Phycomycetes on 

 account of their affinity with the Algae, with which they might naturally be classed 

 as forms without chlorophyll ^ Their thallus, like that of the Siphoneae, consists of 

 unsegmented tubes, in which however transverse septa sometimes appear. The 

 mode of fertilisation is either isogamous or oogamous. The gametes, with the 

 exception of the spermatozoids of Monoblephan's described by Cornu, are not motile. 

 The Ascomycetes are nearly related to this group, as has been already stated in 

 the introduction (p. 8), their archicarps in their simple form showing a very 

 close resemblance to the sexual organs of the Peronosporeae. The difference in 

 Podosphaera, for example, is, that the contents of the female cell (the archicarp) 

 do not form an oosphere as in the oogonium of the Peronosporeae, but the 

 fertilisation takes effect on the still quite small undifferentiated archicarp-cell, 

 which then grows and eventually forms the ascus, after a stalk-cell has first been 

 divided off from it. That the process is more complicated in other Ascomycetes 

 has been stated above. Gonidia also are found in the Ascomycetes answering to 

 those of the Peronosporeae ; the more simple instances of these, as in the Erysipheae, 

 closely resemble what we find for instance in Cystopiis. 



The Uredineae have the same course of development as the Ascomycetes. 

 Their fructifications known as aecidia correspond to the fructifications with asci of 

 the Ascomycetes, only the spores are not formed in asci but by abjunction. The first 

 stages in the development of these fructifications are unknown, but it is probable that 

 they are sexually generated ; beside them a number of gonidial forms are found in 

 the typical Uredineae, and are known as uredospores, teleutospores, and sporidia. 



Lastly, the Basidiomycetes are Fungi, which have no fructifications correspond- 

 ing to an ascus-fructification or aecidium, at least none such are known ; they have 

 only gonidiophores with gonidia which correspond with those in the Uredineae and 

 Ascomycetes. Among the Uredineae too there are species, from whose course of 

 development the aecidium has dropped out, and which are propagated only by 

 gonidia. With the above-named Fungi are associated a few smaller groups, but we 

 will not go further into the detail of their affinities, which are in many points still 

 very doubtful ; among them are the simple forms with which the following account 

 begins^. The order in which the groups are taken is : — 



1. Chytridieae. 



2. Ustilagineae. 



3. Phycomycetes. 



4. Ascomycetes. 



5. Uredineae. 



6. Basidiomycetes. 



* See Sachs, Lehrb. d. Bot., 4th ed. 



^ The account here given has in view only the more important species, in which the develop- 

 ment is more accurately known. 



