Notes. 
267 
clearly. In the youngest stages there appear first to be small groups 
of threads in little secondary pits ; very soon little rounded and bason- 
shaped masses of callus arise in the little depressions on either side of 
the thin membrane, and these finally unite to form a short callus-rod. 
In Wistaria chinensis and in Vi/is vinifera three to five threads 
apparently of the nature of slime-strings have been seen in each 
callus-rod in sieve-plates of this age, but more detailed and careful 
examination is demanded before any conclusive statement can be made. 
In the next older tube the boring out of these strings has proceeded 
further, and given rise to the single slime-string in each callus-rod so 
characteristic of the mature terminal sieve-plates of Angiosperms. 
The views put forward to explain the origin of the callus in species 
of Pinus seem to apply with equal force in the present case : for the 
callus-rods appear to be formed by local alteration of the cell-wall, and 
to arise at first as cylindrical rods, which subsequently become hexagonal 
owing to growth and mutual pressure in the confined area of a pit. 
As to the further production of callus towards the end of the 
season, it would appear that the protoplasm of the sieve-tube 
commences to form callus, which not only builds up the callus-pads 
on the callus-rods of the terminal and lateral sieve-plates, but also 
deposits callus-substance around all the groups of threads which 
connect the sieve-tubes with other elements of the phloem. 
It has become clear during the progress of these researches that 
it is the slime-strings which are of primary importance to the sieve- 
tubes, and that the callus, though no doubt also playing an important 
role in the life-history of the sieve-tube, must be regarded as of 
altogether secondary importance, being for the most part subservient 
to the slime-strings and active or living sieve-tube contents, of which 
the slime-string itself is merely a continuation. 
King’s College, Cambridge, 
Nov . 11, 1902. 
ARTHUR W. HILL. 
* 
NOTE ON THE DISPERSAL OF MANGROVE SEEDLINGS.— 
During the year 1901 and for three months of the present year I was 
engaged in marine biological work for Sir Charles Eliot, K.C.M.G., 
H.B.M. Consul-General at Zanzibar and Commissioner for British East 
Africa. During all this time I was interested in, and at first much 
