THE GROUND BETWEEN ANIMALS AND PLANTS. 653 



potato-disease, instructively as its history bears upon that of other 

 epidemics ; and I have selected the case of the Feronospora simply 

 because it affords an example of an organism, which, in one stage of 

 its existence, is truly a "monad," indistinguishable by any important 

 character from our Ileteromita, and extraordinarily like it in some 

 respects. And yet this " monad " can be traced, step by step, through 

 the series of metamorphoses which I have described, until it assumes 

 the features of an organism, which is as much a plant as an oak or an 

 elm is. 



Moreover, it would be possible to pursue the analogy further. 

 Under certain circumstances, a process of conjugation takes place in 

 the Feronospora. Two separate portions of its protoplasm become 

 fused together, surround themselves with a thick coat, and give rise 

 to a sort of vegetable q^^ called an oospore. After a period of rest, 

 the contents of the oospore break up into a number of zoospores like 

 those already described, each of which, after a period of activity, 

 germinates in the ordinary way. This process obviously corresponds 

 with the conjugation and subsequent setting free of germs in the 

 Heteromita. 



But it may be said that the Feronospora is, after all, a questionable 

 sort of plant; that it seems to be wanting in the manufacturing 

 power, selected as the main distinctive character of vegetable life ; 

 or, at any rate, that there is no pi'oof that it does not get its proteine 

 matter ready made from the potato-plant. 



Let us, therefore, take a case which is not open to these objec- 

 tions. 



There ai'e some small plants known to botanists as members of the 

 genus Coleochcete, which, without being truly parasitic, grow uj)on 

 certain water-weeds, as lichens grow npon trees. The little plant has 

 the form of an elegant green star, the branching arms of which are 

 divided into cells. Its greenness is due to its chlorophyl, and it 

 undoubtedly has the manufactui'ing power in full degree, decom- 

 posing carbonic acid and setting free oxygen under the influence 

 of sunlight. 



But the protoplasmic contents of some of the cells of which the 

 plant is made up occasionally divide, by a method similar to that 

 which effects the division of the contents of the Feronospora-spore ; 

 and the severed portions are then set free as active monad-like zoo- 

 spores. Each is oval and is provided at one extremity with two long 

 active cilia. Propelled by these, it swims about for a longer or 

 shorter time, but at length comes to a state of rest, and gradually 

 grows into a Coleochcete. 



Moreover, as in the Feronosjyora, conjugation may take place and 

 result in an oospore; the contents of which divide and are set free as 

 monadiform germs. 



If the whole history of the zoospores of Feronospora and Coleo- 



