First Part. 



FUNGI. 



DIVISION I. GENERAL MORPHOLOGY. 

 CHAPTER I. Histological Characteristics. 



Section I. The thallus, which in most Fungi is the whole body of the plant 

 not serving directly as an organ of reproduction, begins as a tubular germ-cell 

 {germ-tube, Keimschlauch) which, by continued growth progressing in an apical 

 direction accompanied by repeated formation of lateral branches, developes into a 

 branched body of cylindric thread-like form, the hypha. Both growth and branching 

 follow the laws which prevail generally in the vegetable kingdom. The branching is 

 usually monopodial, in a few cases only it is dichotomous, as in Botryosporium, species 

 of Peronospora, and some Mucorini. 



In some groups, especially the Saprolegnieae, Peronosporeae and the Zygo- 

 mycetes, the thallus or hypha of the Fungus, like the thallus of the Siphoneae, is 

 an unsegmented branched tubular cell up to the time when organs of reproduction 

 are formed. But in the great majority of cases it becomes a branched row of cells 

 owing to the incessant formation of transverse walls concurrently with the growth 

 of the hypha at its apex. The segmentation either takes place only in the apical 

 cell for the time being and at the place of insertion of the FttdimentaryL. branch-k'w^o ^d 

 so that each branch is made up of an apical cell and segment-cells of the first order 

 only, as in Penicillium 1 and Botrytis cinerea, or new intercalary partition-walls are 

 formed in the segment-cells of the first order. 



.In the more simple Fungi the branched hypha alone constitutes the thallus; 

 such forms are termed Hyphomycetes, Filamentous Fungi (Fadenpilze), or 

 Haplomycetes 2 . The body of the largest Fungi, the Mushrooms and Lichens of 

 ordinary parlance, are also composed of hyphae, but their ramifications meet and 

 cohere to form larger aggregates. Such a body, which appears as if formed by the 

 union of Filamentous Fungi, may be termed a compound Fungus-body (zusam- 



[4] 



1 Low in Pringsheim's Jahrb. VII. p. 473. — Brefeld, Schimmelpilze, II. p. 27. 

 a From the Greek word airKoxk, meaning simple. 



