5«3 
Sieve- Tubes of Pinus. 
A comparison of surface-views and sections shows that the 
fine points correspond with plasma-filled pores ; these threads 
thicken later on and increase in length as the wall thickens, 
and appear like his figure in the ‘ Practicum V The threads 
do not stain well with aniline blue in this early stage, but this 
condition soon passes and the fine plasma-threads are changed 
into callus-substance ; with this change the threads become 
thicker and form now the callus rods 2 . 
Referring to the median granules 3 or nodules (Knotchen) 
situated at the middle of active sieve-plates, he inclines as 
before to the view that they are swollen places of the mem- 
brane, so that then their presence must indicate a closing of 
the active sieve-pores. 
In the empty tubes, however, he, like Russow, is unable to 
recognize the median nodules, which is contrary to his former 
expressions of opinion 4 . 
With the change of the threads into callus the highest point 
of sieve-tube function appears to be reached ; the heads of the 
rods soon swell and fuse to form a callus-plate. 
In the ‘one-sided pits 5 between the albuminous cells and 
sieve-tubes he notices that on the sieve-tube side the callus- 
rods reach to the middle lamella, and that on the side towards 
the albuminous cell no callus exists, but very fine threads lead 
from the median granules to the albuminous cells 5 . 
Within the last few days a copy of Strasburger’s latest 
paper on ‘Protoplasmic Connexions 6 ’ has reached me, through 
the kindness of the author, in which he again deals with the 
sieve-plates of Pimis. 
Alcohol material stained with water-blue is used and the 
results agree on the whole with those given in the ‘ Leitungs- 
1 ‘ Bot. Practicum/ 2 te Aufl., p. 146, Fig. 64 A. 
2 Figs. 33 and 34, Taf. ii, ‘ Leitungsbahnen/ should be compared with the 
figures in his * Practicum.’ 
3 ‘ Leitungsbahnen/ p. 71. 
4 ‘ Bot. Practicum/ See back also, p. 582. 
5 ‘ Leitungsbahnen/ Figs. 6-9, Taf. i; Fig. 35, Taf. ii. Jahrb. f. wiss. Bot., 
Bd. xxxvi, Heft 3, Taf. xiv, Fig. 28. 
6 Strasburger, ‘ Ueber Plasmaverbindungen pflanzlicher Zellen/ Jahrb. f. wiss. 
Bot., Bd. xxxvi, Heft 3, pp. 523-526, Figs. 21-28. 
