244 



GYMNOSPERMS 



the conifers, leaf traces are similarly connected with the bottom and 

 sides of the broad fusiform ray. 



Bars of Sanior Many botanists believe that the ''bars" or "rims" 

 of Sanio are reliable criteria in determining alhnities. Sanio/^^ ^s 

 long ago as 1873, found thin spots in the young cellulose walls of 

 tracheids of Pinus sylvestris, and around the thin spots, a thickened 

 border. The thin spots he called Primordialtupfcln and the thickened 

 borders, Umrisscn. The Umrisscn have been called the bars of Sanio. 



Groom and Rushton"^ called them 

 rims, a better translation of Sanio's 

 term (fig. 251). 



It is now known that the marginal 

 portion of the primordial pit does 

 not thicken like the rest of the cell 

 wall. While the rest thickens by a 

 deposit of lignin, the rim begins to 

 thicken by a deposit of pectin and, 

 later, by a deposit of lignin, so that 

 the pectose part is overlaid by lignin. 

 It was claimed that the bars con- 

 sisted of cellulose, but the presence 

 of pectose seems established by chemical tests. In their reaction 

 to stains the bars behave more like pectin than cellulose, staining 

 so intensely with safranin that the stain can be drawn from the 

 lignified parts and still leave a bright red in the bars, making them 

 look like superficial structures. 



In passing from the pith to the mature wood, the rims become 

 more separated from the pits and there is a tendency to fuse, so that 

 the structure looks more like a bar than a rim. The bar appearance 

 is even more pronounced when there are two pits side by side. 



Miss Gerry found, in i9io*°7 the bars or rims of Sanio in all 

 families of conifers except the Araucariaceae, and concluded that 

 the presence of bars in coniferous wood indicated Abietacean affini- 

 ties, while their absence indicated Araucariacean affinities. But 

 later, in 191 2, Jeffrey,*"" found bars in the cone axis of four species 

 of Araucaria and concluded that their presence in such a conserva- 

 tive region indicated an ancestry in which bars were normally pres- 



FiG. 250. — Pinus strobus: longi- 

 tudinal section of a cone axis, show- 

 ing a tracheid bent along a ray. — 

 After Thompson.' '5 



