Sieve-Tubes of Finns. 603 
persist and form the nodes or median dots of the connecting 
threads. 
When the formation of the sieve-tubes of Pinus is con- 
sidered, it is seen that they arise by tangential division from 
the cambium, and therefore it is especially in the tangential 
walls that threads or their rudiments would be expected to 
occur. 
In order to see if this was the case, numerous sections of 
tissues of all ages preserved in various ways have been 
examined, but with at present very little result ; so that it is 
possible that the nodes may get obliterated very quickly, and 
only have an ephemeral existence in the developing cell-wall. 
It is quite likely, however, that they do occur in the walls, but 
that owing to imperfect methods of fixation or staining and 
the delicacy of the tissues, their presence has not yet been 
demonstrated. Their apparent absence does not in any way 
invalidate the theory which has been put forward, for the 
obliteration of threads owing to mucilaginous degeneration 
has been proved to be a phenomenon of common occurrence h 
The Function of the Connecting Threads and 
Slime-Strings. 
Theories as to the probable functions of connecting threads 
have frequently been put forward by previous investigators, 
which are in the main true, although in some cases the real 
threads on which their theories are based have never been seen. 
The value of the threads for the transmission of stimuli, and as 
paths for the passage of water and substances in solution, has 
been discussed and supported by special examples in the former 
paper, and there seems to be nodoubtthattheconnecting threads 
are all-important for transmitting stimuli from cell to cell 1 2 . 
With reference to their function in translocation, it is 
difficult to bring forward direct proofs of their value, since 
their small size makes it almost impossible for any direct 
1 As, for instance, in the walls of the separating palisade-cells and other tissues. 
Cf. Hill, loc. cit., Figs. 7 and 11. 
2 Cf. Gardiner, Czapek, &c. 
