Some new evidence on the physical nature of plant nuclei from intra-specific polyploids

Abstract

The object of this paper is to make clear certain facts regarding the resting nuclei and mitotic phenomena of plants. These facts are of material importance to both experimental and morphological cytologists, but so far do not seem to have been clearly appreciated by either. Indeed, the extreme diversity of outlook between the two branches of what should be one science may easily be shown by a simple quotation from current text-books of each. Thus Gray (1931), on p. 122 of his “ Text-Book of Experimental Cytology,” remarks: “ Since all nuclei exhibit a visible granular or fibrillar structure after coagulative fixation, it is generally supposed that the structures seen as preserved preparations or in moribund nuclei are to be regarded as purely artificial products of coagulation, which cannot be correlated with the fundamental structure of a living nucleus. This view, developed many years ago by Hardy, is now accepted by the majority of animal cytologists.” Sharp, on the other hand, in the new edition of the “ Introduction to Cytology ” (1934), on p. 54, remarks: “ These results [from plants], together with the analogous findings of Chambers on the prophases in animal spermatocytes, indicate that the reticulum appearing in a well-fixed nucleus fairly represents a delicate thready structure actually present during life and rendered more distinctly visible by fixation.” While admitting, as will be shown, the inadequacy of the “ reticulum ” conception as a complete description of any nucleus, it must be confessed that the entirely negative view of “ the majority of animal cytologists ” comes as nothing less than a shock to anyone familiar with the degree of precision and certainty of which plant cytology is becoming increasingly capable. This precision is generally recognized where it concerns the morphology and behaviour of chromosomes in the definitive state. To deny all validity to the morphological approach to the resting nucleus appears, in contrast, both unjustified and undesirable. It is undesirable, owing to the very obscurity of most nuclei in the living state; a state so difficult to observe and interpret that every possible source of information should be exploited. That such excess of caution is also unjustified may perhaps become more apparent from the new evidence to be presented. This admittedly deals with dead cells, but the type of reasoning is such that it does not depend for its validity on the detailed interpretation of fixation alone. It may therefore help to bridge the gap between the morphological and experimental fields of observation.