Recent and Fossil Conifer a, 143 



tubes parallel to its axis, the contained membranes are easily 

 seen. 



Lojigitudinal Sections. — The elegance of the reticulated tex- 

 ture displayed in the transverse section of many of the Conifer®, 

 must arrest the attention of every observer ; but it is in the 

 longitudinal section parallel to a radius, that we are to look for 

 the most beautiful mechanism the Coniferae display. To cut 

 such a section, however, in a proper manner, is often attended 

 with some little difficulty, arising from the different degrees of 

 hardness on the opposite sides of each annual layer. The sec- 

 tion must be parallel to a radius. It must be nearly of an uni- 

 form thickness, and neither too thick nor too thin. If too thick, 

 the structure of the parts does not come into view, and if too 

 thin, only a shadow of the whole remains. 



Such a section, when seen with a proper magnifying lens, pre- 

 sents the longitudinal vessels with their bounding partitions 

 well defined. The vessels are generally widest at the inner side 

 of each annual layer, and gradually diminish in that respect to- 

 wards the outer edge. Near the latter they are often so narrow 

 that the partitions almost touch one another. In some parts 

 the vessels are often rectilinear to a considerable extent, and in 

 other parts they often assume a curvilinear form, and even in- 

 osculate or cross one another. At irregular intervals the ves- 

 sels are often traversed at right angles by bundles of straight 

 lines more or less numerous, and these may often be seen 

 stretching across several annual layers without interruption. 



In every species of the family of Coniferae, whether they con- 

 tain annual layers or not, the longitudinal vessels, as seen in the 

 longitudinal section parallel to a radius, are in some places ap- 

 parently empty, but in other places they contain groups of cir- 

 cular objects more or less numerous. These objects, or discs as 

 they may be called, are of different dimensions in different 

 species, and in every case where there are annual layers they are 

 always of the greatest diameter at the inner side of each layer. 

 They diminish in size towards the outer side, and when the 

 vessels become very narrow they generally disappear. The 

 discs are often pretty regular circles, especially when they are 

 situated at a certain distance from each other, but they some- 

 times become slightly elliptical especially when near one another. 



