602 
Hill. — The Histology of the 
The portions of the peculiar lenticular patches in which 
these threads occur are* however, a good deal swollen, and 
appear to be but slightly removed from callus-substance, and 
it seems a reasonable view to consider that this swollen portion 
of the membrane is composed of a substance intermediate in 
composition between cellulose and callus 1 . 
The state of the albuminous cell-sieves thus makes it clear 
that it is only from the sieve-tubes that the influences, which 
so affect the character of the connecting elements, can 
emanate, and moreover, as was implied earlier in this paper 2 , 
it seems evident that the sphere of influence of each sieve-tube 
only extends to the limits of its own cell-wall, that is to say, 
as far as the median nodes of the connecting threads. 
Between the sieve-tubes and bast-parenchyma cells of Finns 
there are no connecting threads 3 , so that the albuminous cell 
thread-groups are the only means of protoplasmic union between 
the sieve-tubes and the parenchymatous tissues of the phloem. 
The Distribution of the Threads. 
In the former paper 4 the general distribution of the connecting 
threads was discussed especially with reference to their abun- 
dance in the radial wallsof the various tissues. In the phloem this 
arrangement is even more conspicuous, for all the sieve-tube 
and albuminous-cell ‘ threads ’ occur in the radial walls, and 
only the medullary-ray cells possess them in their tangential 
walls ; thus no direct communication by means of threads can 
take place between an older and younger sieve-tube in the 
same radial row. 
According to the views recently put forward by Gardiner 5 
threads, or their rudiments, should be visible in all cell-walls, 
since the nodes of the achromatin fibres of the nuclear spindle 
1 Cf. Hill, loc. cit., Fig. 37 ; cf. also the hydrated cellulose of Tamus , v. p. 596. 
2 Cf. Fig. 9, PI. XXXII, and Figs. 17-20, PI. XXXIII, where the alteration of 
threads in the sieve-plates is seen to proceed from both sides of the membrane 
towards the middle lamella. 
3 Hill, loc. cit., p. 110, and Fig. 24, PI. XXXIV. 
4 Loc. cit., p. 1 1 9. 
5 Gardiner, Roy. Soc. Proc., 1900. Various examples are brought forward 
to show, in some cases, all the nodes prolonged as threads, or all overlaid, or else 
some nodes overlaid while the others are continued. 
