RECENT ADVANCES IN VEGETABLE CYTOLOGY. 25 



organisms in which we as yet have failed to recognise a de- 

 finite nuclear body, for there are reasons for believing that the 

 nuclear substance is in all cases really present, whether it 

 happens to be collected into a specialised mass or not. And 

 it should be remembered that the number of cells supposed 

 to possess what we may term a distributed or discrete 

 nucleus is becoming smaller as our means of investigations 

 improve. Thus according to Wager ( 1 ) even Bacteria 

 possess a true nucleus. 



I am perfectly aware that attacks have recently been 

 made on the cell-theory as extended to explain the organisa- 

 tion (Whitman, Sedgwick) of animals, and that nobody 

 would assert the cell to the ultimate unit of living substance. 

 But neither of these propositions really affects, or is con- 

 cerned with, the point of view just now before us. We are 

 not here dealing with the wide questions connected with the 

 architecture of the organism as a whole, nor with the 

 equally difficult one, as to what constitutes the ultimate 

 units of living matter, rather we are content just now to 

 study the interaction of the parts which together are capable 

 of carrying on a continuous living existence, which form a 

 living individual, and these parts consist jointly of the 

 nucleus and its surrounding cytoplasm. 1 The occurrence of 

 cell walls is a matter of no importance from a general stand- 

 point, although when present they may profoundly modify 

 the characters of the organism in which they are formed. 

 Many plants are known in which the protoplasm is only 

 delimited by a cell wall from the surrounding medium, while 

 the oftentimes huge protoplasmic mass suffers no internal 

 partitioning, although it contains a vast number of nuclei 

 distributed through it. 



Sachs, with characteristic insight, long ago perceived 

 that the presence or absence of cell walls is a matter of 

 only secondary importance. Their sequence and arrange- 

 ment at the time of their first appearance can be predicted 



1 The researches of Klebs, Acqua, and others have shown that although 

 protoplasm deprived of a nucleus may sometimes even assimilate food and 

 maintain life for a not inconsiderable period of time, it is incapable of 

 division. 



