370 BOTANY PART n 



same natural group and is thus not necessarily connected with the commencement of 

 a new generation. In certain Brown Algae and in all Archegoniatae the reduction 

 takes place in the sporangia so that the gametophyte is regularly haploid and 

 the sporophyte diploid. The nuclear difference cannot, however, be regarded as 

 determining the specific structure of the alternating generations. 



The reproductive cells (swarm-spores, gametes) of the classes of Thallophyta 

 which can be derived from the Flagellata are in many cases ciliated, naked proto- 

 plasts resembling the cells of Flagellates. Even in the Bryophyta and Pterido- 

 phyta, and also in the Cycadeae and Ginkgoaceae, the male gametes, though 

 also secondarily modified, exhibit this return during the ontogeny to the phyletic 

 original form. 



CLASS I 

 Bacteria ( l > 3 - 9 ) 



Bacteria are unicellular or filamentous organisms of very simple 

 construction. Chlorophyll is wanting in them, and their mode of 

 life is usually a parasitic or saprophytic one. A large number 

 of species exist distributed over the whole earth, in water, in the 

 soil, in the atmosphere, or in the bodies of dead or living plants and 

 animals. They are often termed Fission Fungi, or Schizomycetes, 

 since the multiplication of the unicellular forms takes place by a 

 division into two and the separation of the segments. This mode 

 of multiplication is also found in other unicellular plants. 



The cells of the Bacteria are surrounded by a thin chitinous 

 membrane, and contain a protoplasmic body, which is usually 

 colourless, and can be made to contract away from the membrane 

 by plasmolysis. The protoplasm may contain one or more vacuoles. 

 One or several granular structures are also present in the protoplast ; 

 these so-called chromatin bodies may be deeply coloured by stains, 

 and have been regarded as nuclei by various authors. Since, as yet, 

 undoubted karyokinetic division has not been observed in these 

 bodies, the presence of nuclei in the bacterial cell cannot be regarded 

 as certainly established. 



For the most part the Bacteria are extraordinarily minute organ- 

 isms, and probably include the smallest known living beings. The 

 spherical cells of the smallest forms are only 0*0008 mm. in 

 diameter; the rod-shaped cells of the tubercle bacillus are only 

 0*0015-0*004 mm. long, while most species are about 0*001 mm. 

 broad and 0*005 mm. long. 



The simplest forms of Fission Fungi are minute spherical 

 cells, COCCI. Forms consisting of rod-shaped cells are designated 

 BACTERIUM or BACILLUS. Kod-shaped forms with a slight spiral 

 curvature are called VIBRIO, and those more strongly curved SPIRILLUM. 

 The unicellular cocci, rod-shaped forms, and vibrios may also remain 

 united in chains after the cell division. Frequently the cell membranes 



