STRUCTURE.] SCHLEIDEN HENFREY. 91 



wholly wanting. They are largest in plants having milky 

 juice, and smallest in those whose juice is transparent. 



Plate II. contains representations of several laticiferous 

 vessels. Fig. 16. shows them thin-sided and filled with latex. 

 Fig. 17. represents them thick-sided and filled with latex. 

 Fig. 39. shows them empty. At fig. 12. a, and g, they are 

 seen parallel with the other tissue, filled with latex, and a 

 little contracted at intervals. 



The analogy between laticiferous tissue, and the other 

 forms, is not well made out. Schleiden declares that he is 

 not quite satisfied as to its cellular origin, and regards that 

 question as being uncertain. He describes cinenchym thus : 

 " It resembles large intercellular passages ; no proper mem- 

 brane is visible, but it may be so thin as to escape our 

 observation. What is very remarkable however is, that at 

 the juncture of two adjacent cells, where there must be an 

 intercellular passage, as in all true cells, there should still be 

 no membrane visible ; in old isolated vessels, depressions and 

 sharp angles are clearly visible, whence it is clear that the 

 vessels must have been closely pressed by the surrounding 

 cells. The vessels are generally so numerous and anastomose 

 so much, that it is hardly possible to trace them along their 

 whole course ; this may, however, be done by dissolving the 

 surrounding tissue in nitric acid. Without such a con- 

 trivance, they can generally be seen to stretch across the 

 whole of a part of a plant, but then they often terminate 

 abruptly, especially in the side branches ; this is remarkably 

 evident in leafless Euphorbias, and one cannot help wondering 

 how there can be any dispute about the matter. On the sides 

 of old vessels, especially in the stems of leafless Euphorbias, 

 spiral streaks and layer-like thickenings can be seen, so that 

 the gradual development of these formations agrees entirely, 

 thus far, with that of cells." (Grundzuge, 2nd edit. p. 254.) 



Mr. Henfrey regards it as " intercellular passages which 

 become lined by a proper membrane " but such appearances 

 as are represented at Plate II. fig. 19, seem to be irreconcilable 

 with his hypothesis. 



I believe the laticiferous tubes to be strings of cells united 

 at their ends, and with the partitions absorbed. The common 



