trace of spiral direction (still some of these vessels unroll spirally), 

 and it has been found in their development, that the granules do not 

 arrange themselves in a simple line at first, but that they adhere to 

 each other in such a manner that all the branches of the fibre, that 

 interlace with each other and leave meshes between them, proceed in 

 their development at the same time ; much like the growth of Hydro- 

 dictyon utriculatum, either beginning at one end of the vessel, and 

 proceeding spirally towards the other, or beginning lengthwise and 

 extending around the interior of the membranous tube, the several 

 ends of the fibres being simultaneously growing points.* 



In the dotted vessel the ramifications of the fibre are most frequently 

 irregular, and are formed in the same manner as in the reticulated ves- 

 sel. In the development of the fibre in the Exogenic vessel, which 

 can be well examined in the young shoots of the willow, I have found 

 that the development proceeds much in the same manner as before 

 described, viz., by the granules adhering each to another in various 

 beaded lines, so as to form a fibre or deposit of a reticulated arrange- 

 ment, the meshes of which correspond to the dots on the surface, as 

 in the way described. There is one singular character belonging to 

 the dots on this vessel which distinguish it from the preceding, which 

 is, that every dot has a central mark or smaller dot, usually of a sin- 

 gularly red colour, and which, when highly magnified, appears as a 

 minute garnet set in the centre of each dot ; and by this structure 

 these markings approach those on coniferous wood, and I believe 

 them to be of the same nature, from gradual transitions observed in 

 the vessels of Zamia Altensteinii, and figured by Link in his * Philo- 

 sophia Botanica.' This red colour is owing to the dot being some- 

 what hollowed or cupped, and the centre being only thin membrane, 

 and the passage so small for light to be transmitted, that it becomes 

 decomposed ; if charred very black and immersed in Canada balsam, 

 this view is rendered perfectly satisfactory by its appearing the most 

 transparent point. 



In the Endogenic vessel, the connecting branches are given off 

 under each other, so that the dots, which are here also rounded, are 



* In the marked vessels it very often happens, though I helieve never in spiral ves- 

 sels, that the ends which are opposed to each other in two contiguous vessels are ab- 

 sorbed, so that a communication exists between them. In the dotted vessel it is most 

 commonly that one aperture exists and the termination is rather dilated and suddenly 

 acuminate. In the Exogenic, Endogenic and Scalariform, between the union of the 

 vessels the membrane is absorbed and the fibres remain, so that several apertures ex- 

 ist (sometimes resembling a "grating") between the junction of two vessels. 



