276 Hill . — The Histology of the Sieve-Tubes of Anglo sperms. 
same condition as in February and March, for the callus showed sharp con- 
tours, and no slime-strings were present. The pores of the old strings were 
seen only with difficulty and often appeared as dotted lines crossing the 
callus owing to the remains of the disintegrated portion of the slime-strings 
(Fig. 54, PL XVIII). By about April 20 the phloem again became active 
and the slime reappeared in the sieve-tubes and began to force its way through 
the old pores in the callus-masses. The callus had as yet undergone 
scarcelyanychange and preserved a firm and definite outline (Figs. 55 and 56, 
PI. XVIII). By the beginning of May a great change was found to have 
taken place : the slime-strings had all been re-established and the callus had 
lost its sharp outlines and would not stain very deeply with the usual re- 
agents, owing no doubt to the action of the ferments, which were actively 
engaged in its solution (Fig. 57, PI. XVIII). At the end of May the sieve- 
plates were found to be practically in the normal summer condition, with the 
callus forming a delicate lining to the pores through which the short thick 
slime-strings passed (cf. Fig. 9, PI. XVII, and Text-fig. 8, j.i-). 1 
Sieve-Tubes crossing the Medullary Rays. 
Wilhelm 2 was the first to describe and figure the short cross-connecting 
sieve-tubes in Vitis vinifera , which traverse the medullary rays and join 
one group of sieve-tubes with another. 
Similar anastomosing strings of sieve-tubes were noticed by Russow 
in Quercus pedunculata. Those of Vitis are again described and figured by 
Lecomte, 3 whose figure is reproduced in Perrot’s treatise. 4 
These cross-connecting bands or strings of sieve-tubes are composed of 
small elements, each being about the size of the adjacent parenchymatous 
cells, and there seems every reason to believe that they represent ordinary 
medullary-ray cells, which have undergone special development (Text-fig, 13). 
It is unfortunate that, owing to the difficulty of finding these cross- 
connexions in sections of young material, their development has not been 
able to be studied in detail ; for it seems probable that interesting informa- 
tion might be obtained as to the formation of slime-strings from the original 
thread-groups of the parenchymatous cells which serve as the mother-cells 
of these short sieve-tubes and companion cells. 
The sieve-plates of these sieve-cells are essentially similar to those of 
the ordinary sieve-tubes, and show well-developed callus-pads. 
1 At the beginning of April the winter buds had begun to swell, and the Vine bled on being 
cut. Towards the end of the month the buds were bursting, and by May 9 the young shoots were 
one to two inches in length, and there was no ‘ bleeding’ of the Vine on cutting. On May 16 one 
of the leaves of the young shoot had unfolded. Root pressure becomes active some three or four 
weeks before any visible changes take place in the phloem. 
2 Wilhelm, 1 . c., PI. VI, Fig. 69. 3 Lecomte, 1 . c., PI. XXIII, Fig. 40. 
* Perrot, Le Tissu crible, p. 42, Fig. 24. 
