182 PLANT PHYSIOLOGY 



If the nucleus were larger and the cytoplasm proportion- 

 ally abundant, if the permeability of the enveloping mem- 

 branes and their tensile strength were proportionally in- 

 creased, if the absorbent power (osmotic force) of the cell 

 were also raised proportionally, is there any reason why the 

 cell, the organ, and the organism should not grow larger? 

 The question cannot be answered. Many organisms do not 

 attain larger size when, so far as we can now see, it would 

 be possible for them to do so. Are the bacteria so small be- 

 cause they have so little nuclear substance in proportion to 

 cytoplasmic? .On the contrary some authors* have claimed, 

 from the behavior of bacterial cells toward staining agents, 

 that they are mainly nuclear substance with but a thin layer 

 of enveloping cytoplasm. The amount of room and of food 

 which the individual bacteria could occupy and consume 

 would certainly suggest that they might attain larger size. 

 Their enveloping membranes appear to be sufficiently per- 

 meable and strong for larger organisms. Yet the bacteria 

 remain minute, and no reasons now known can account for 

 their size. If our mechanical explanations fail on these organ- 

 isms, are they any more certain to be correct when applied 

 to the growth of larger ones? What limits the size must 

 have to do with the sensitiveness, the irritability, of the 

 living matter, and this leads us to the subject of the next 

 chapter. 



* See in Migula's System der Bakterien, Bd. I., pp. 72-80, the discussion 

 of this point and the references pro and con. 



