PHYSIOLOGICAL 321 



Some recent work on parasitic worms has, however, raised again 

 the doubt whether they are so really anaerobic as they seem to be. 

 Thus Slater, working on Nematodes, has shown experimentally 

 that the worms do not thrive in the absence of oxygen — they have 

 merely great endurance; it follows that they must normally get 

 oxygen from somewhere, and most probably from the blood of the 

 host. It has been shown that dyes dissolved in the blood of the host 

 may find their way into the tissues of the parasite, and it is likely 

 that oxygen may be transported in a similar way. All this makes 

 it seem doubtful whether any animals can survive absence of oxygen 

 except by passive resistance. 



MOVEMENTS OF PLANTS 



Some of the simplest plants, as among the unicellular or few- 

 celled Algae, have flagella or lashes of living matter, by means of 

 which they propel themselves through the water. One of the phases 

 in the life-history of the Slime Fungi, if they are regarded as 

 plants, is flagellate; and it is succeeded by a less active, but also 

 motile, amoeboid phase. Many bacteria move rapidly by means of 

 numerous cilia. The threadlike Oscillarias, consisting of a single 

 row of cells, are able to sway about in the water and to creep 

 along a substratum — an early instance of the co-operative activity 

 of cells. The flinty-shelled diatoms, which form a very important 

 part of the microscopic plankton — the food of many pelagic animals, 

 move about in a somewhat puzzling way, probably by the emission 

 of very delicate protoplasmic threads. Many spores among the lower 

 plants are actively mobile in water, and sperm-cells with cilia or 

 flagella occur not only in ferns and mosses and their relatives, but 

 as high up in the scale as Cycads and Maiden's Hair trees. More 

 fam liar are the movements of climbing plants and of some of the 

 insectivorous forms like the sundew. 



But even when all the many cases of plant movement are con- 

 sidered, the well- justified impression remains, that plants are 

 characteristically different from animals in expending relatively 

 little energy in locomotion or external work. They use most of their 

 energy in growth and in internal work. It is just saying the same 

 thing in another way if we emphasise the fact that the ratio of 

 constructive or anabolic processes to disruptive or katabolic pro- 

 cesses is always much greater in a green plant than in an animal of 



(A a\ 



about the same size and weight ( j^ much greater than 7 ]• A con- 

 sequence, which also helps as a cause, is the enclosing of the plant- 

 cell in a wall of cellulose, which must greatly hinder mobility. There 

 are often streaming movements within a cell, and diffusion move- 



VOL. I Y 



