CONJUGATE. 41 



and the root is reduced to a mere watery pulp. This organism 

 generally infects the plant through a wound, but it is able to 

 enter the epidermis of undeveloped leaves. 



Pseudomonas campestris produces a brown discolouration of 

 the vascular tissue in the roots and leaves of Cruciferous plants. 

 It attacks the woody portion of the vascular bundles, and is 

 found in great numbers blocking up the wood- vessels. The in- 

 fection of the leaves may take place through the water-pores, and 

 spreads thence along the vascular bundles to other parts of the 

 plant. 



Pseudomonas Tiyacinthi is pathogenic to Hyacinths, spreading 

 especially through the vascular system. Yellow spots are found 

 on the bulbs and foliage which are due to the vessels becoming 

 filled with a yellow mucilage produced by the Bacteria. 



Bacillus solanacearum attacks the Tomato, Egg-plant, and 

 Potato, causing the withering and final death of the young 

 shoots. 



Bacillus betce gives rise to the " Gummosis " of the Sugar 

 Beet, 



Micrococcus tritici is an organism which infects the grain of 

 Wheat, and preys upon the proteids and starch, forming what is 

 known as " Pink Wheat." 



Bacillus mali, it has lately been shown, is the cause of the 

 cankers so common on the Apple and Pear. This parasite is pro 

 bably carried by Aphides, and effects an entrance through the 



wouuds caused by these insects. 



Class 5. Conjugatae. 



The Alga3 belonging to this class have chlorophyll, and pyre- 

 noids round which starch is formed. The cells divide only in one 

 direction, they live solitarily, or united to form filaments which 

 generally float freely (seldom attached). Swarm-cells are want- 

 ing. TJie fertilisation is isogamous (conjugation} and takes place 

 by means of aplano gametes. The zygote, after a period of rest, 

 produces, immediately on germination, one or more new vegetative 



