Sl^RUCTURE OF PROTOPLASM 43 



The body of the protoplast, the protoplasm as we may call it, is built 

 up of organs and elemental structures. The nucleus is an organ of very 

 general importance, and indeed, a separation into nucleoplasm (karyo- 

 plasm) and cytoplasm probably occurs in all protoplasts 1 . On the other 

 hand, chromatophores, including chlorophyll corpuscles, are organs of 

 special character, and are absent from fungi. When such special organs 

 are present they may be given the general name of plastids 2 . 



Like all living substance the plasmatic organs are of considerable 

 complexity. This is readily perceptible in the resting nucleus, and is 

 admirably shown when the latter divides, while the chromatin fibres, 

 which are then so markedly visible, may also be seen to have a definite 

 structure of their own. Besides the plastids already mentioned, the 

 cytoplasm may contain minute bodies, often in great numbers, which, 

 regardless of their morphological and physiological nature, may be termed 

 microsomes or microsomata. They may be composed in some cases of 

 non-living substance, but in other cases may be minute living plastids 3 . 



But few of the organs and structural elements of which the proto- 

 plasm is composed are visible even with the highest powers of the 

 microscope ; nevertheless we must of necessity conclude on theoretical 

 grounds that all living material is built up of most minute living units. 

 The gradual progress and increase of our knowledge of the visible 

 structure of plants renders the existence of smaller organs and elements 

 certain, although these still remain to be discovered. Indeed it is not 

 impossible that there are organisms, or developmental stages of minute 

 but visible organisms, which the highest powers of the microscope fail to 

 reveal to us. 



In a small cell, or one of the organs of such a cell, the component 

 units must necessarily be still smaller, and yet have positive dimensions ; 

 while the smaller and more numerous these units are, the more varied 

 and complicated will the possible combinations be. At the same time a 

 relatively greater surface area is correlated with the smaller size, and this 

 is a factor of the utmost importance ; for bacteria teach us what remarkable 

 powers are conferred by extreme minuteness, and what extraordinary 

 processes it renders such organisms capable of performing. 



Ideas of size abstracted from the visible world will hardly enable 

 us to realize either the infinitely great or the infinitely small, but 



1 On schizophytes, see Hegler, Botan. Centralbl., 1895, Bd. LXIV, p. 203; A. Fischer, Jahrb. 

 f. wiss. Bot., 1895, Bd. xxvn, p. 150; Nadson, Botan. Centralbl., 1895, Bd. LXIU, p. 238, &c. ; 

 Palla, Jahrb. f. wiss. Bot., 1893, Bd. XXV, p. 511; Zimmermann, Morphol. und Physiol. d. Zell- 

 kernes, 1896, p. 160; A. Fischer, Unters. iiber Cyanoph. und Bacterien, 1897, pp. 6r-i2i. 



2 The term ' plastid ' is used in a variety of ways. See Zimmermann, Pflanzenzelle, 1887 ; Wiesner, 

 Elementarstruktur, 1892, p. 83; Schutt, Peridineen, 1895, p. 74. 



3 Hanstein, Das Protoplasma, 1880, p. 22. 



