597 
Sieve- Tubes of Pinus. 
The Origin of the Callus. 
But to return again to the main subject, the development 
and mode of growth of the callus 1 now requires to be con- 
sidered more closely, since two distinct views as to its mode 
of formation are held : 
1. That it is due to mucilaginous degeneration of the cell- 
wall ; and 
2. That the protoplasm alone is concerned in the formation 
of callus. 
The first of these two divergent views is due to Wilhelm 2 , 
who was supported by Janczewski 3 , and later by Oliver 4 , 
who in his paper on the sieve-tubes of Laminaria brought 
forward a strong case in proof of the cellulose origin of the 
callus. 
On the other hand, the protoplasmic origin of the callus 
has the support of Russow 6 , with whom it originated, Stras- 
burger 6 , and Fischer 7 , whilst Rendle 8 adopts a middle 
course and believes that the callus (which he describes in the 
‘ vesicular vessels } of the onion) may be derived both from 
the cell-wall and from the protoplasm ; and lastly, Moore 9 
brings forward a different theory, for he considers the callus 
to be proteid in nature and therefore of protoplasmic origin. 
The facts brought to light during the present research 
make it appear highly probable that the middle course 
between these two opposed theories, as is so often the case, 
represents the true state of affairs, namely, that the callus may 
be formed both by alteration of the cellulose cell-wall and by 
1 For the bibliography of the subject see Zimmermann, Bot. Mikrotechnik, 
•where references to Mangin’s papers are given. 
2 Wilhelm, Beitr. zur Kenntniss d. Siebrohren-Apparates d. dicot. Pflanzen, 1880. 
3 Janczewski, loc. cit. 4 Oliver, Ann. Bot., vol. i. 
5 Russow, loc. cit., 1882. 6 Strasburger, ‘Bot. Bract.,’ 1884. 
7 Fischer, Ber. d. Deutsch. Bot. Ges., 1885, &c. 
8 Rendle, Ann. Bot., vol. iii. Rendle’s results appear to be of great interest, and 
it is hoped shortly to examine the vessels of the onion by our methods, in order to 
see if there is any connexion between the callus-patches and groups of connecting 
threads. 
9 Moore, Journ. Linn. Soc., vol. xxvii, 1891. Moore’s results do not appear to 
have received any confirmation. 
R r 2 
