§ XIV.] Diseases in lower animals and in plants. 177 



becoming lobed, and that the Cornalian bodies are produced in 

 them by endogenous formation. It follows from analogy with 

 other better-known Sporozoa, that the Cornalian bodies would 

 be spores, and that their germination gives rise to the amoeboid 

 protoplasmic bodies in which fresh spores are formed in large 

 numbers. The extreme delicacy of such amoeboid protoplasmic 

 bodies as these sufficiently explains why it was so long before 

 they were clearly made out, especially when they had penetrated 

 into and were enclosed in the tissue of the insect's body which 

 is also protoplasmic. 



Hence the parasite of p^brine must also be excluded from 

 consideration in a treatise on Bacteria ; nor would so much 

 have been said about it here, if it did not serve to show in a 

 very instructive manner, not only that very minute parasites 

 which are not Bacteria are the contagium in infectious diseases 

 in animals, but that we may be dealing with organisms of a quite 

 different kind, conformation, and mode of life from Bacteria, 

 even when the figures before us are very like Bacteria and are 

 easily mistaken for them. 



2. Lastly, parasitic Bacteria do not often appear, according 

 to our present experience, as the'contagia of diseases in plants (77). 

 Most contagia of the many infectious diseases in plants belong 

 to other groups of animals and plants, the larger number to the 

 Fungi proper, as was observed on pages 146, 147. 



Among cases of the kind we may mention first the yellow 

 disease studied by Wakker, which destroys hyacinth-plants. 

 Wakker found that the most characteristic symptom in this 

 disease is the appearance of a rod-shaped Bacterium, 2-5 \i, long 

 and a fourth or half as broad, which aggregates into slimy yellow 

 masses filling the vessels and tissue of the vascular bundles 

 in the bulb-scales during the time when vegetation is dormant. 

 At flowering time these masses ascend also into the leaves, 

 where they are not confined to the vascular bundles, but make 

 their way from them into the intercellular passages and into the 

 cells of the parenchyma, stopping up the passages and destroying 



