26 FIRST GROUP. THALLOPHYTES. 



Bacillus subtilis 1 , the species which has been most thoroughly investigated, will 

 serve to illustrate the course of development, so far as it is known, in the Schizomycetes. 

 It is one of the commonest species and lives naturally in fluid and semi-fluid substances. 

 Its germs, like those of all Schizomycetes, become disseminated when the substratum 

 dries up ; they rise into the air and are borne along by its currents. This species 

 exists in the vegetative condition in the form of small rods, about twice as long as 

 broad, which multiply by bipartition, the divisions either soon separating or cohering in 

 the form of slender filaments. Each little rod can during its vegetative period assume 

 the motile condition, and then has two delicate cilia, one at each extremity; single 

 filaments also may become motile. As soon as the nourishing substratum is exhausted, 

 growth and division cease, and fructification begins by the formation of a spore in each 

 rod in the following manner. Clearer points make their appearance in the middle of 

 a rod, or towards an extremity, pointing to a denser accumulation of protoplasm at 

 the spot. The whole cell-contents of the rod now gradually draw together to this spot 

 and assume the form of an ovoid or oblong-cylindrical strongly refractive mass, which 

 invests itself with a cell- wall from within outwards and so becomes a spore. After the 

 spore is formed the rod swells slightly at the hyaline spot ; by-and-by the other parts 

 of the rod disappear. In germination the spore becomes paler in colour at first and 

 increases in size. Then exactly in the middle of the side of the somewhat elongated 

 spore, a protuberance (the germ-tube) makes its appearance and lengthens rapidly, and 

 soon separates by transverse division into daughter-rods. 



The spores are so small, that their nature as vegetable organisms cannot be 

 recognised by their outward appearance. They germinate immediately, requiring to 

 pass through no period of rest. On the other hand, as Brefeld has shown, they offer 

 unusual resistance to external influences. They are killed by boiling only when the 

 process is continued for two hours ; a shorter time, such as a quarter of an hour, only 

 excites them to more abundant germination. They are not readily affected by poisonous 

 substances, though their development is hindered by addition of acids, especially 

 mineral acids. Formation of spores has been ascertained to take place in a number of 

 other Schizomycetes, e.g. in Bacillus Amylobacter, Vibrio Riegiila, Eacilhis Ulna"*, and 

 is in fact a very general phenomenon, though the mode of proceeding sometimes varies 

 slightly from that given above for Bacillus subtilis. 



IV. ALGAE 3 . 



Under the term Algae are here included all the Thallophytes which contain 

 chlorophyll, with the exception of the Cyanophyceae and Diatomaceae ; in two sections 

 only of the Algae is the chlorophyll masked by another colouring matter. The Algae 

 are not grouped together on account of this physiological character, but because the 

 course of development of their forms, varied as it is, is yet essentially the same, the 

 extreme forms being connected together by intermediate ones. The vegetative 

 structure of the thallus is not less varied than the mode of sexual propagation ; in 



1 See Brefeld, Unters. iiber die Schimmelpilze, Heft IV. 



2 Prazmowski, Zur Entwicklungsgeschichte und Fermentwirkung einiger Bakterienarten (Bot. 

 Zeit. 1879, p. 409). 



3 A succinct account of this group has lately been published by Falkenberg (Schenk's Handbuch 

 der Botanik, II. Bd.). [See also Wille, Zur physiol. Anat. d. Algen (Bot. Centralbl. Vol. XXI. 1884), 

 for a summary of investigations into the construction of Algae ; also Ferd. Hauck, Die Meeres 

 Algen (Rabenhorst, Crypt. Flora v. Deutschland, 2nd Ed., Leipzig, 1883, Schmitz, Fr., Die Chroma- 

 tophoren in Algen (Verh. d. naturh. Ver. Preuss. Rheinl. u. Westph. 1883), and Beitr. z. K. d. 

 Chiomatophoren (Pringsh. Jahrb. XV. 1884).] 



