5 8 PHYSIOLOGICAL MORPHOLOGY 



SECTION 10. Uni- and Multi-nucleate Cells. 



In every cell a nucleus is constantly present, but in many cases more 

 than one, and in some cases a very large number may be found. The 

 latter is always the case in unicellular plants of considerable size, such as 

 the Siphoneae (Multinucleatae), Mucorinae, and Myxomycetes. Unicellular 

 tissue elements may also be multinucleate, as is the case, for example, in 

 those laticiferous tubes which are derived from a single cell. The division 

 of the nucleus is not always necessarily followed by the division of the cell, 

 and it is by the continued division of the nucleus, unaccompanied by corre- 

 sponding cellular division, that multinucleate cells are produced. 



Even when no cellular division occurs, the nuclear segments separate 

 from one another, and distribute themselves regularly throughout the cell so 

 that no large portion of the cytoplasm is without a nucleus associated with it. 

 This is the reason why isolated fragments of the plasma of Vancheria, 

 Mucor, &c., can regenerate the entire plant, for since in such plants the 

 nuclei are very small and numerous, an exceedingly small fragment may 

 still contain a nucleus, and hence be capable of regenerating the entire 

 plant. Whether in such cases the small size of the nuclei is of importance 

 in tin's respect, or whether this minuteness is connected in some way with 

 the absence of cellular division 1 , is impossible at present to say. 



The multinucleate nature of large cells ensures that the necessary and 

 important interactions between the nucleus and the particular portion of 

 cytoplasm with which it is connected do not need to be transmitted 

 through too great an intervening space. In this way the multinucleate 

 cell attains the sanie ends as do the small uninucleate cells forming a tissue. 

 It is not known what is the utmost distance across which the nucleus and 

 cytoplasm may interact and influence one another, and the distance 

 a stimulus may be transmitted through a living tissue, multiccllular and 

 therefore multinucleate also, has no bearing on the point at issue. In 

 cytoplasmic fragments which are able to secrete a cell-wall owing to their 

 being connected with a nucleated protoplast by a delicate plasmatic thread, 

 we have an actual example of a stimulating influence, affecting a particular 

 function, being transmitted across a distance amounting, in some cases, to 

 several millimetres 2 . 



Experiments of a similar character to those made by Townsend may 

 possibly throw further light on these and other related questions. Any 

 large uninucleate cells which may occur in a tissue are generally adult 

 and fully grown, and are hence no longer called upon to exercise all the 

 primitive functions of which a cell is capable. Very possibly, in such large 



' Cf. Strasburger, Histologische Beitrage, 1893, Bd. V, p. 124. 



3 Townsend, Inaugural dissertation, Leipzig, p. 19, 1897 (Jahrb. f. wiss. Hot., 1897). 



