RECENT ADVANCES IN VEGETABLE CYTOLOGY. 29 



possible to account for the fact that in certain embryos 

 which have been mutilated, the surviving cells are enabled 

 to so modify the course of their normal development as 

 to make good the loss, and thus to form a perfect, if 

 somewhat miniature organism ? For had there been no 

 mutilation the cells thus concerned would unquestion- 

 ably not have developed in the same way, but would have 

 fulfilled the allotted task of merely providing for the genesis 

 of their normal tissue products. Or again, why is it that 

 when a lizard's tail is broken off the general form of the 

 entire animal is once more reproduced, even though there 

 are important histological and structural (but probably not 

 functional) differences in the new tail as compared with 

 that of the original one (4) ? 



When differentiation has so far become manifested in 

 an organism that the limits of the several energids are 

 coterminous with the cell walls, a considerable increase in 

 their degree of independence doubtless ensues, but it is, as 

 already stated, by no means absolute, and the examples just 

 quoted support the statement. Whether organisation is 

 the result of, or the factor which determines, the co-ordi- 

 nate action of the cells is a question which we may safely 

 leave to the future to decide. But perhaps it may be 

 permissible to compare the cell colony which forms the 

 organism to an isolated society in which the caste system 

 prevails. Each caste or cell group is predestined to dis- 

 charge certain definite offices in the state or the organism. 

 If some indispensable caste should become exterminated, it is 

 obvious that a differentiation and displacement must occur 

 amongst those which survive, and this differentiation 

 might either be readily complete, or it might only arise as 

 a reluctant concession to necessity, just as a willow twig 

 planted upside down in damp soil will form roots at this, its 

 upper, end ; though comparison with a twig planted with 

 its basal end in the ground will show how severe a tax the 

 unusual effort has proved. 



It has already been said that an energid, and it might 

 also be added, a typical cell, consists essentially of a nucleus 

 and the protoplasm included within a certain area around 



