136 



BOTANY 



PAKT I 



The traces of the axillary buds of most Gymnosperms and 

 Dicotyledons unite to form two strands which enter the mother shoot 

 and are inserted ujion its leaf-traces (Fig. 143 /:). 



As a general rule, the leaf-trace bundles in Gymnosperms and 



Dicotyledons arrange them- 

 selves in a circle in the stem. 



in 



There are, however. Dicotyle- 

 dons in which the vascular 

 bundles form two (Cucurbita, 

 Phytolacca, Piper) or more circles 

 (Amaranflms, Pajxirer, ThaUctrum). 

 In such cases the inner circle 

 is usually more or less irregular. 

 In the stems of Monocotyle- 

 dons (Fig. 137) the vascular 

 bundles are scattered, and with- 

 out any apparent regular order. 



^fn 



S//I 



•HI 



I 



Fig. 145. — Clematis viticella. End of a branch 

 wliicli lias been made transparent by the le- 

 moval of the superficial tissues and treatment 

 with caustic potash. The emerging strands 

 have been slightly displaced by gentle |)ressure. 

 The two uppermost pairs of young leaves (W ', 

 bl 2) are still without leaf-traces, v, Apical cone. 

 (After Nageli.) 



//« 



Fig. 146. — Diagram showing the course of 

 the vascular bundles of Monocotyledons 

 of the Palm type, with alternating two- 

 ranked amplexieaul leaves. The numbers 

 indicate the sequence of the leaves ; m, 

 median bundle. (After Ue Bary.) 



Their scattered arrangement is due to the varying distances to which 

 the bundles of the leaf-traces penetrate into the central cylinder of the 

 stem. This results from the prolonged growth in thickness of the 

 growing point after the first procambial strand has been laid down, 



31 



