PARASITISM IN PLANTS AND ANIMALS. 291 



we shall one day bo released from the material bonds in which 

 we are here "cribbed, cabined, and confined," that we shall 

 throw off the tough envelopes of this mundane, transitional ex- 

 istence, and breathe at last " an ampler ether, a diviner air." 



Absteact op Lecture, No. 5. — Germs. By H. De Havilland, 

 Esq., of Cambridge University. 



If a potato plant be grown in the dark, a white shoot is the 

 result, and when the store of food laid up in the potato is used 

 up, the existence of the white plant is at an end. The obvious 

 inference is that white plants are incapable of forming their own 

 food from such materials as are suflScient for their gi'een rela- 

 tions, whose chief food is the carbonic acid gas in the atmosphere. 



When men ascend great heights they find a difficulty in breath- 

 ing, the air is becoming more and more scarce ; there is thus 

 evidently only a certain quantity of air available for animals to 

 breathe. How is it then if, as we know is the case, the air is 

 being continually contaminated by the carbonic acid exhaled 

 from the animal lungs that the whole air, in the long course of 

 the centuries during which life has been on the earth, has not 

 become overwhelmingly carbonic acid in constitution, and all 

 animal life at an end. The answer is found in the fact already 

 mentioned, that green plants absorb the carbonic acid for their 

 own use, and — this is the important point — return the pure 

 oxygen to the air. Sunlight is a necessity for this process of 

 purification ; without it plants behave as animals. So that while 

 plants in the day time may be of distinct value in a sitting room 

 as purifiers of the air ; in the bed room they are in their wrong 

 place, especially if in any quantity. 



Examples of white plants or fungi are very numerous : the 

 mushroom flower, the toadstool, puff balls among the larger 

 ones ; the well-known moulds appearing on damp pairs of boots, 

 the mould so frequently found on badly preserved jams, and the 

 mildew of wheat are only a few of the better known ones of 



