23 



II. — On Multimccleate Cells : An Historical Study {1879-1919), 

 ^j Rudolf Beer and Agnes Arber. 



{Bead February 18, 1920). 



"The idea of the cell, as the fundamental unit in the bodies of all 

 organized beings, has now become so deeply ingrained into all our 

 biological thought, that there is a danger of our treating the cell- 

 theory and its associated corollaries rather as rigid axioms than as 

 truths which are still in process of disclosure. It is, after all, only 

 eighty years since the publication of Schwann's epoch-making 

 ■*' Microskopische Untersuchungen," and it may be well to remind 

 ourselves from time to time that the history of the cell-theory has 

 been so brief that our general notions of the construction of the 

 -cell and of the relation of its parts must, for many years to come, 

 be open to criticism and revision. 



For more than a century and a-half after the first discovery by 

 Hobert Hooke of the cellular structure of plants the attention of 

 microscopists was almost exclusively devoted to the cell membrane. 

 It was not until 1833 that Robert Brown observed a nucleus in 

 the cells of a number of plant tissues, his earliest records relating 

 to certain orchids. This discovery marks the first step towards a 

 proper appreciation of the protoplasmic content of the cell as its 

 <essential component. The conception of the typical cell as a uni- 

 nucleate structure is often treated at the present day as if it were 

 a self-evident proposition, the truth of which could be established 

 on a priori grounds. It should be remembered, however, that it is 

 really an idea which was arrived at inductively by the earlier 

 cytologists, and which rests entirely on accumulated observations. 

 It was Nageli, in 1844, who first definitely formulated the now 

 familiar view as to the uninucleate character of the vegetable cell. 

 He concluded, from his extensive researches, that, with the 

 'exception of cells in the act of division, pollen grains, pollen tubes 

 and embryo sacs, each element contains only a single nucleus. 

 Further research has modified and elaborated the list of organs that 

 oome under the head of Nageli's exceptions. The literature of 

 botany for the three-quarters of a century which has passed since 

 his work was published includes extensive references to the 

 appearance of the multinucleate character in the structures to 

 which he refers, and also in the pro-embryo of the Gymnosperms, 

 suspensor cells, tapetal tissues, etc. But his central conception of 



