THE PALM-STEM. 27 



The course of development of these vessels, which I 

 investigated in the germinating date-palm, in the apex of 

 the stem of Rhapis flabelliformis, and in the root of 

 many species of Palms, and with which the development 

 of the large vessels of Dioscorea, Tamus elephantipes, &c., 

 fully agrees, is as follows : In young shoots, we find in 

 the situation where the large vessels subsequently lie, 

 perfectly closed, large, and cylindrical tubes, which are 

 composed of a colourless and very delicate membrane. In 

 tubes a little older, we find a network of very delicate, 

 transparent fibres upon the internal surface ; these have 

 a horizontal direction, are connected at places which cor- 

 respond to the longitudinal septa of the adjacent cells by 

 perpendicular and oblique fibres. As a general rule, the 

 horizontal fibres are so arranged that they are not con- 

 tinuous over several lateral walls of the vessel, but termi- 

 nate where they reach a longitudinal septum of an adjacent 

 cell, and here pass into a fibre, going obliquely upward 

 or downward, so that a mesh of a fibrous network comes 

 as a direct successor of the fibre on the adjoining side- 

 wall of the vessel. From this it is most clear that these 

 vessels are not originally spiral vessels, the fibres of which 

 become reticularly connected by the subsequent develop- 

 ment of cross-fibres. This is made still more evident by 

 the fact, that in the first origin of the fibrous network, 

 we in many cases meet with the fibres only perfected at 

 particular places, the walls of the vessel appearing still 

 perfectly smooth in other situations. The older the vessel 

 grows, the broader and thicker its fibres become, and 

 the interspaces between them are diminished in width in 

 proportion, till at last they display themselves as mere 

 narrow slits. The septa are perfected in a manner wholly 

 analogous, but the original delicate membrane is generally 

 destroyed, after a time, in the interspaces of the fibrous 

 network. 



are produced by a protruding expansion (a kind of hernia) of the adjacent 

 cell, which penetrates the pore, and either tears through or causes the 

 absorption of the primary membrane of the vessel. 



