24 president's address. 



organs have l)een discovei'cd on the roots, stems, and leaves of plants, 

 which, like tlie otocysts of some animals, appear to be really ' statocytes,' 

 and to exert a varying pressure according to the relations of these parts of 

 the plant to gravity. There is apparently something resembling a per- 

 ception of the incidence of gravity in plants which reacts on irritable 

 tissues, and is the explanation of the phenomena of geotropisra. These 

 results have grown out of the observations of Charles Darwin, followed 

 by those of F. Darwin, Haberlandt, and Nemec. 



A few words must be said here as to the progress of our knowledge of 

 cell-substance, and what used to be called the i3rotoplasm question. 

 We do not now regard protoplasm as a chemical expression, but, in ac- 

 cordance with von Mohl's original use of the word, as a structure which 

 holds in its meshes many and very varied chemical bodies of great 

 complexity. Within these twenty-five years the ' centrosome ' of the cell- 

 protoplasm has been discovered, anfl a great deal has been learnt as to 

 the structure of the nucleus and its I'emarkable stain-taking bands, the 

 chromosomes. We now know that these bands are of definite fixed num- 

 ber, varying in diflierent species of i^lants and animals, and that they are 

 halved in number in the reproductive elements — the spermatozoid and 

 the ovum — so that on union of these two to form the fertilised ovum 

 (the parent cell of all the tissues), the proper specific number is attained. 

 It has been pretty clearly made oui: by cutting up large living cells — ■ 

 unicellular animals— that the body of tne cell alone, without the nucleus, 

 can do very little but move and maintain for a time its chemical status. 

 But it is the nucleus which directs and determines all definite growth, 

 movement, secretion, and reproduction. The simple protoplasm, de- 

 prived of its nucleus, cannot form a new nucleus — in fact, can do very 

 little but exhibit irritability. I am inclined to agree with those who 

 hold that there is not sufficient evidence that any organism exists at the 

 present time which has not both protoplasm and nucleus — in fact, that 

 the simplest form of life at pi'esent existing is a highly complicated struc- 

 ture — a nucleated cell. That does not imply that simpler forms of living 

 matter have not preceded those which we know. We must assume that 

 something more simple and homogeneous than the cell, with its differen- 

 tiated cell-body or protoplasm, and its cell kernel or nucleus, has at one 

 time existed. But the various supposed instances of the survival to the 

 present day of such simple living things — described by Haeckel and others 

 — have one by one yielded to improved methods of microscopic examination 

 and proved to be differentiated into nuclear and extra-nuclear substance. 



The question of ' spontaneous generation ' cannot be said to have 

 been seriously revived within these twenty-five years. Our greater 

 knowledge of minute forms of life, and the conditions under which they 

 can survive, as well as our improved microscopes and methods of 

 experiment and observation, have made an end of the arguments and 

 instances of supposed abiogenesis. The accounts which have been pub- 

 lished of 'radiobes,' minute bodies arising in fluids of organic origin when 



