28 THE CELL 



certain Monocotyledons {e.g. Tradescantia) by Johow is the result of 

 the fragmentation of a single primary nucleus; this disintegration is a 

 senile phenomenon, and is probably devoid of any special physiological 

 significance. 12 



A protoplasmic organ which is so conspicuous and so universally 

 distributed as the nucleus must undoubtedly play a highly important 

 part in the Life of the cell ; as a matter of fact, numerous investigators 

 have been striving, during the past three decades, to gain further 

 insight from various points of view into the functions of the nucleus. 13 



The majority of biologists at the present day regard the nucleus 

 as the vehicle of the hereditary characters of the organism; in other 

 words, the nucleus is supposed to contain the hereditary substance or 

 idioplasm. 



It was Nageli, who, in the year 1884, first enunciated a theory, 

 supported by ingenious arguments, to the effect that the protoplasm of 

 every germ-cell must contain a comparatively solid and excessively 

 complex germ-plasm or idioplasm; this substance initiates and 

 regulates the "predetermined and specific developmental activity 

 that results in the formation of cell-complexes of varying size, of a 

 specific plant, of a root or of a hair pertaining to a specific plant." 

 Every recognisable property of the completed organism is present in a 

 rudimentary form in the idioplasm ; the latter substance is, of course, 

 not confined to the germ-cells, but occurs also in every somatic cell of 

 the developing organism, initiating and directing its specific activities. 



Nageli pictured the idioplasm to himself as existing in the shape 

 of a system of delicate strands, which form a continuous network 

 penetrating into every part of the plant-body; but he hazarded the 

 suggestion that this substance " is more especially aggregated within the. 

 nucleus." Soon afterwards this tentative hypothesis gave place to the 

 theory which regards the idioplasm as located exclusively in the nucleus. 

 This conception again may be traced back to Nageli, who pointed 

 out that the offspring in general derives its hereditary morphological 

 features to an equal extent from both parents, in spite of the fact that 

 the bulk of the female gamete, or egg, is usually many thousand times 

 greater than that of the male gamete, or sperm. If, however, the capacity 

 for inheritance possessed by the idioplasm is equally great in the case of 

 both male and female gametes and there is no reason to suppose 

 the contrary, it follows that equal quantities of idioplasm must be 

 present in the two kinds of gametes, however greatly the latter may 

 differ in respect of the total bulk of the protoplast. The question 

 then arises, as to what part of the sperm contains the idioplasm. 

 Since the cilia and the other cytoplasmic portions of the male gamete 

 are adapted for the performance of special physiological functions, it 



