178 ANIMALS AND PLANTS. [LECT. 



There is reason to think that certain organisms 

 which pass through a monad stage of existence, such 

 as the Myxomycetes, are, at one time of their lives, 

 dependent upon external sources for their protein 

 matter, or are animals ; and, at another period, manu- 

 facture it, or are plants. And seeing that the whole 

 progress of modern investigation is in favour of the 

 doctrine of continuity, it is a fair and probable 

 speculation though only a speculation that, as 

 there are some plants which can manufacture protein 

 out of such apparently intractable mineral matters as 

 carbonic acid, water, nitrate of ammonia, metallic and 

 earthy salts ; while others need to be supplied with 

 their carbon and nitrogen in the somewhat less raw 

 form of tartrate of ammonia and allied compounds ; 

 so there may be yet others, as is possibly the case with 

 the true parasitic plants, which can only manage to 

 put together materials still better prepared still more 

 nearly approximated to protein until we arrive at 

 such organisms as the Psorospermice and the Pan- 

 histophyton, which are as much animal as vegetable 

 in structure, but are animal in their dependence on 

 other organisms for their food. 



The singular circumstance observed by Meyer, 

 that the Torula of yeast, though an indubitable 

 plant, still flourishes most vigorously when supplied 

 with the complex nitrogenous substance, pepsin ; the 

 probability that the Peronospora is nourished directly 

 by the protoplasm of the potato-plant ; and the won- 

 derful facts which have recently been brought to light 

 respecting insectivorous plants, all favour this view ; 



