GROUP 1. THALLOPHYTA : FUNGI. 275 



species of Typhula and Agaricus), it is effected by bodies termed 

 sclerotia ; each sclerotium consists of a compact mass of hyphae, 

 filled with reserve materials, covered by a cortex of one or more 

 layers of cells, which are thick- walled, and of a dark colour. They 

 become detached from the mycelium on which they are formed, 

 and are capable of retaining their vitality during a long dormant 

 period ; on germination they give rise to shoots bearing reproduc- 

 tive organs. 



A form of sclerotium is found also in the Myxomycetes. Here 

 it consists of a plasmodium, or a part of a plasmodium, which has 

 surrounded itself with a membrane, and remains for a longer or 

 shorter time in a dormant condition. The individual amoeboid 

 cells may also surround themselves with a membrane and remain 

 dormant, in the form of microcysts. 



Reproduction is effected sexually or asexually. A sexual process 

 takes place in the Zygomycetes ; in the Peronosporacese ; and ap- 

 parently in some Ascomycetes, though this is a matter of con- 

 troversy. 



The modes of the sexual process are the following : 



I. Isogamy : sexual cells, similar aplanogametes which are not 

 set free ; process, conjugation ; product, a zygospore ; Zygo- 

 mycetes. 



II. Heterogamy : 



a. Oogamy : sexual cells, oospheres and undifferentiated male 



cells (spermatozoids in Monoblepharis ?) ; process, fertili- 

 sation ; product, an oospore ; Peronosporaceee, Ancylistaceae. 



b. Carpogamy : no differentiated female cell j female organ 



fertilised either by (1) the undifferentiated contents of the 

 male organ (e.g. Eremascus, Pyronema); or (2) by differenti- 

 ated male cells, spermatia (e.g. Collema) : product, a fructifi- 

 cation termed an ascocarp : all the forms in which this mode 

 occurs belong to the Ascomycetes. 



There is no sexual process in the Schizomycetes, the Myxomy- 

 cetes, in some of the Phycomycetes (Saprolegniacese), the great 

 majority of the Ascomycetes, the JEcidiomycetes, and the Basid- 

 iomycetes. In the Schizomycetes and Myxomycetes, the absence 

 of a sexual process may be attributed to their rudimentary charac- 

 ter; in the higher groups it is due to sexual degeneration. In 

 the Saprolegniaceae, female and, generally, male organs are deve- 



