THE NUCLEUS 27 



in accordance with the form of the cell-cavity. More rarely the nucleus 

 is lobed, as in the pollen-grains of various Angiosperms, or provided with 

 slender pointed prolongations, as in the foliar epidermis of Ornithogalurn 

 umbellatum, in the petiolar hairs of Pelargonium roseum and P. zonale, 

 and in the digestive cells of mycorrhizal organs, such as the roots 

 of Neottia Nidus avis or the rhizomes of Psilutum, In many of these 

 instances the unusual shape of the nucleus is obviously correlated with 

 the special nature of its functions ; but further discussion of this point 

 must be postponed. 



The size of the nucleus is partly a specific character, which remains 

 constant within certain limits of affinity ; but it is also to some extent 

 dependent upon the particular physiological function of the cell or 

 tissue. The first point may be illustrated by the following examples. 

 Relatively large nuclei occur generally among Conifers and Monocoty- 

 ledons, while these structures are remarkably small throughout the 

 Fungi. Among Dicotyledons, the Eanunculaceae and Loranthaceae 

 are distinguished by the possession of comparatively large nuclei. As 

 regards the variation in the size of the nuclei in different tissues, 

 prominence may be given to the fact that large nuclei are especially 

 characteristic of meristematic tissues, in which, according to Strasburger, 

 the diameter of the nucleus amounts on an average to two-thirds of 

 the width of the entire cell. As a matter of fact, Schwarz has shown 

 by careful measurement that the nuclei of meristematic ceils become at 

 first even larger, when the latter are transformed into adult elements, 

 but that their size gradually diminishes again as the growth of the 

 cell comes to a standstill. 11 Sachs was long ago led to attribute an 

 administrative function to the nucleus, on account of its relatively 

 large size in the case of meristematic cells. Glandular cells also as a 

 rule possess comparatively large nuclei, a circumstance which again 

 suggests that it is the nucleus which controls the metabolic activity of 

 the cell. 



The typical vegetable cell is uninucleate. Treub has shown that 

 in Higher Plants several nuclei, or even a large number of these struc- 

 tures, occur in the elongated fibres and latex-tubes of various species 



Of EUPHORBIACEAE, ASCLEPIADACEAE, APOCYNACEAE, and URTICACEAE, 



doubtless on account of the unusual size of the cells in question. For 

 whatever the special functions performed by the nucleus may be, it is 

 clearly an advantage for a protoplast of more than ordinary dimensions 

 to possess, in place of a single large nucleus, a number of equivalent 

 organs of smaller size distributed evenly throughout the cell. The 

 multinucleate " cells " characteristic of certain Algae and of a great 

 many Fungi must be regarded in a similar light. On the other hand, 

 the multinucleate condition of aged parenchymatous cells observed in 



