igo GYMNOSPERMS 



follows, as it usually does, many leaves fall, and those remaining on 

 the tree do not reach their full size and are likely to fall early in the 

 autumn. Such an untimely swelHng of the buds is usually accom- 

 panied by the formation of a growth-ring; not a strong ring which 

 might cause uncertainty in estimating the age, but nevertheless a 

 ring which can easily be seen. 



Mucilage cavities are abundant. They are found in the pith and 

 in the primary cortex of the stele, in the root, in the petiole and blade 

 of the leaf, in the seed and its peduncle, and in the sporangium. They 

 seem to be absent from the secondary cortex. Tannin cells and cal- 

 cium oxalate crystals are also abundantly and widely distributed. 



The vascular cylinder of the stem is an endarch siphonostele. The 

 protoxylem consists exclusively of spiral elements, which are much 

 more abundant in the spur shoots than in the long shoots. In the 

 long shoots, in transverse section, in the radial direction, there are 

 from one to five spiral elements; while in the spur shoots there may 

 be as many as ten, with five or more quite common. In both shoots, 

 the spiral elements border directly upon the pitted tracheids. 



The tracheids of the secondary wood have one or two rows of 

 bordered pits on the radial walls, not crowded as in the Cordaitcs 

 group, but more or less scattered. Their arrangement is either 

 opposite or alternate. The last tracheids of a year's growth have 

 tangential pitting, where they border upon the spring wood of the 

 next year, a feature of considerable interest, because paleozoic stems 

 of the Cordaitcs type, when they have rings, do not show any radial 

 pitting. 



Bars of Sanio are easily demonstrated in the secondary wood, 

 but do not occur in the primary wood^°' (tig. 203). The pits are 

 often so scattered that no bars are formed. The trabeculac of Sanio 

 also occur, but are easily distinguished from the bars, because they 

 cross the lumen of the tracheid, while the bars are covered by a 

 secondary thickening of the cell wall. 



The medullary rays are characteristically short in vertical extent, 

 many of them being only one cell in height, and they are nearly al- 

 ways only one cell in width. Rays one cell wide and two cells high 

 predominate in the trunk and in the long shoots, but some rays are 

 three, four, or even live cells in height. In the spur shoots the rays. 



