60 



MORPHOLOGY OF SPERMATOPHYTES 



ducts are schizogenous in origin, a group of glandular cells 

 being formed by repeated division, which separate by the split- 

 ting of common walls, and organize a passageway which they 

 line, and into which they pour their characteristic secretion. 



The chief histological features of the Conifer stem may be 

 summarized as follows: (1) growth in diameter by means of 

 the primary cambium cylinder, (2) secondary xylem radially 

 arranged and composed entirely of tracheids with bordered pits, 

 (3) presence of resin ducts, and (4) absence of companion cells. 



THE LEAF 



The occurrence of foliage leaves and scales is far from uni- 

 form, as was indicated in the discussion of the stem, and may be 

 outlined in a general way as follows: (1) foliage leaves only, 

 as in most Cupresseae and in Araucarieae ; (2) scale leaves only, 

 as in Phyllodadus (the spur shoots being transformed into 

 phylloclads) ; (3) both foliage leaves and scales, either on the 



FIG. 44. Taxus laccata : .7, branch with ripe seeds; #, ovule projecting beyond scales 

 of the small fertile branch ; ,?, longitudinal section of #; ^, young seed not yet in- 

 closed by aril ; 5, longitudinal section of ripe seed ; <?, Thuja orientalis ; 7-0, Junip- 

 erus communis. After KERNER. 



same shoot, as in Abies and its allies, or on different shoots, as in 

 Pinus. It was noted in connection with the stem that spread- 

 ing needle leaves on all the shoots is probably the primitive 

 Conifer condition, and that the scales and other leaf forms have 

 been derived from them. 



The foliage leaves are quite variable in form, from small 



