5 6 PHYSIOLOGICAL MORPHOLOGY 



same insect on different plants might be expected to differ markedly from 

 one another 1 . 



In the protoplast, the nucleus and cytoplasm exhibit a variety of 

 activities, and the inherent connexion and relationship between the two are 

 much more intimate than they are between two distinct but adjacent cells 

 of a tissue. The nucleus and cytoplasm live in closest symbiosis, and it is 

 possible, and indeed probable, that an exchange of living substance or of 

 physiological units may take place between them 2 . It has not yet been 

 definitely determined whether, or to what extent, any exchange of spindle- 

 threads, centrosomes, nucleoli, &c., may take place between the nucleus 

 and cytoplasm. In certain stages of nuclear division, according to some 

 authors, no definite boundary exists between the nucleus and cytoplasm 3 ; 

 the nuclear membrane being absorbed. 



Though a knowledge of perceptible results forms the primary and 

 essential basis of scientific research, still we must never fall into the error 

 of supposing that we see the actual operating causes in the movements or 

 changes of shape, &c., which may accompany, or apparently initiate, the 

 final result (cf. Sect. 8). Identical results may be produced by widely 

 different means ; and hence the general resemblance between karyokinetic 

 figures and magnetic lines of force 4 in no wise indicates that the former 

 are produced in a similar manner to the latter. Although the visible 

 phenomena of nuclear- and cell-division are the result of invisible changes 

 and forces, it still remains of interest and importance to establish if possible 

 accurate comparisons with allied phenomena. It can only be decided by pro- 

 longed experimental research whether the occurrence of amitotic cell-division 

 is always an accurate indication that in such cells something is wanting 

 which cells undergoing mitotic division possess 5 . Recent studies have 

 shown that the processes of nuclear and cell-division do not always neces- 

 sarily follow exactly the same course, and even if no living animal of the 



' For a summary of our knowledge on this subject, see Eckstein, Pflanzen-gallen und Gallen- 

 thiere, 1891. 



1 [Huie (Quart. Journ. of Micros. Science, XXXIX, 1897, p. 387, 'Changes in the cell-organs of 

 Drosera'} states that in a stimulated gland-cell a portion of the cytoplasm disappears, and con- 

 cludes that it is replaced by the nucleus absorbing food material, metabolising it, and excreting it 

 into the plasma. The staining reactions on which these conclusions are based, however, hardly 

 suffice to establish this theory.] 



3 Cf. Zacharias, Flora, Erganzungsband, 1895, p. 253; Zimmermann, Beihefte z. Botan. 

 Centralbl., 1894, Bd. IV, p. 86, and the literature here given. [Also Sargant, Annals of Botany, 

 1896, p. 445.] 



4 Cf. Errera, Compt. rend. d. 1. Soc. Royale d. Botanique de Belgique, 1890, Bd. XXIX, p. 17. 



8 Hegler, Bot. Centralbl., 1895, Bd. LXIV, p. 203; Zimmermann, Beihefte z. Bot. Centralbl., 

 1893, Bd. in, p. 353; Strasbnrger, Histologische Beitrage, 1893, Heft 5, p. 99. According to 

 Gerasimoff (Ueber die kemlosen Zellen bei Conjugaten, 1892, p. 9) the application of cold causes 

 mitotic division which has already recommenced to become reversed, the nucleus becoming normal 

 again, whilst subsequent division takes place amitotically. [This is readily explicable if the forma- 

 tion of mitotic figures is simply an indication of great nuclear activity.] 



