Lecture XL 85 



out the whole organism. In Vaucheria we find numerous nuclei 

 indicating the organic centres of as many cells but the continuity 

 of the cytoplasm of all the cells being merged in an unbroken 

 film is more complete than in Volvox. Such structures as this, in 

 which many cells are fused, the cytoplasm being continuous and 

 the whole covered by a common cell-wall, are called ccenocytes. 



It may be appropriately recalled here that investigation has 

 shown that the cells of bacteria do not possess a characteristic 

 nucleus, so that we have again to revise our conception of a cell 

 and we may define it as a more or less isolated and independent 

 mass of protoplasm usually differentiated into a nucleus and 

 cytoplasm and often possessing a cell-wall. 



A search by means of suitable reagents will soon convince one 

 that starch is absent from Vaucheria. This immediately indicates 

 that a difference exists between its metabolism and that of the 

 other green plants which we have hitherto examined. 



It will be observed, however, that when exposed to light, 

 oxygen is evolved from the green branches and this evolution 

 does not occur if the surrounding water is deprived of carbon 

 dioxide. During this process the oil droplets grow in bulk. Evi- 

 dently photosynthesis is taking place, but instead of a production 

 of starch going on as a result of this, oil is being formed. Inas- 

 much as oils possess a smaller proportion of oxygen than carbo- 

 hydrates, evidently the volume of oxygen evolved will be greater 

 than that of the carbon dioxide absorbed, in place of being equal 

 to it as is the case when a carbohydrate is formed. It is only 

 protoplasm furnished with chlorophyll that can carry on photo- 

 synthesis and hence this function is not discharged by the 

 colourless rhizoids but only by the green branches. Owing to 

 the position of the rhizoids, which are covered over by the green 

 branches and embedded between the particles of sand and grit, 

 they are cut off from the light and so, even if they possessed 

 chlorophyll, could not carry on photosynthesis. Hence they have 

 come to act as organs of attachment for the plant, while the 

 function of photosynthesis is assigned to the rest. There is thus 

 a division of labour between the parts of this organism. The 

 absorption of nitrates, so far as we are aware, may be carried on 

 all over the surface of the ccenocyte. 



No excretory organs of any kind are known. As has been 

 pointed out, the presence of a continuous cell-wall precludes the 

 development of a contractile vacuole. Also the working up again 

 into new protoplasm of any nitrogenous waste produced seems 

 a characteristic of vegetable metabolism. Carbon dioxide is, 



