A MANUAL OV THE CONIFERS. 



point at each end. The spiral vessels much resemble the woody fibrous 

 ceUs, but with their membranous walls much thinner, and "enclosing a 

 spiral fibre coiling more or less regularly within its thin tube from on 

 extremity to the other."* These spiral coils are now known to contain 

 air, and play an important part in the functions of the plant, especially 

 in connection with the transmission of the sap; they are found in the 

 leaf-stalks of most of our large trees, as the Lime, Maple, &c. 



Now the minute parts of the stem of a Coniferous tree, as the 

 Pine or Fir, are found to differ from those of other trees in the 

 following particulars — 



1. The tubes have a diameter much greater than that of the 

 wood cells of any other class of Exogenous trees. 



2. They alone transmit the sap upwards,! which is 

 very abundant. 



3. There are in general no true vessels; rows of 

 vascular cells, which occur only in the medullary 

 sheath, taking their place. $. 



4. There are marked on the sides of the tapering 

 wood cells, towards the medullary rays, a peculiar set 

 of dots or circular disks. 



These dots were supposed to be 

 minute glands between the adjacent 

 tubes or cells, and the woody fibre 

 in which they were found was called 

 the glandular form of that fibre. But 

 recent investigations have shown that 

 their presence is owing to the want 

 Kg. 3. Tiausyerse section of uniformity in the increase in the 

 thickness of the cell walls, and that 



B 



of two wood cells of Scotch 

 Fir, each with a pore, "«" 



£££££•.?& Ml at certain spots, pitted or. cell pores 

 SS.^featoftZSWK are formed > the membrane between 

 x'^«RSdta the ceUs di sa PP earin g. ancl the ceUs 

 ceU is 'of 2 ' scotch Thom& becoming actually perforated. In 



Fir, with bor- Coniferous wood these pore cells are widened at their base, 



dered pits; mm L .. 



pores connecting rendering them comparatively easy to be detected under the 



the cells of the . ° __ L n , ,„ i ■, ■., i, « -n- o 



wood with those microscope. They are called "bordered pits. See Jbigs. 2 

 rays, x about and 3. " The characteristic position of the pits which, in 

 Thom6° pl ° om the cells of the stems, are usually arranged in one ; in 

 those of the roots, often in several rows, as well as that 

 of the resin passages, form an excellent diagnosis to distinguish th.c 

 different kinds of wood."S 



Dr. Carpenter, Vegetable Physiology, § 53. t Idem, § 51. 



Thome's Structural Botany, p. 371. § Idem, p. 372, 



