152 



THE STEM PROPER 



returned to be distributed to the other organs. Even the 

 roots can not be fed by the Uquid they absorb from the soil 

 until it has been elaborated in the leaves, just as our 

 bodies can not be sustained by what we eat and drink until 

 it has been digested in our stomachs. Hence, if the leaves 

 of a tree are diseased or destroyed by ignorant pruning, 

 the roots will suffer and die just as the leaves do if the 

 roots are injured. 



On account of this double line of communication which 

 they have to maintain, the vascular threads, or bundles, as 

 they are technically called, are double; one set, composed 

 of larger ducts, carrying water up, and another set of 

 smaller ones bringing back the digested food. Can you 

 give a reason for their difference in size .i" 



216. Woody Monocotyledons. — Examine sections of 

 yucca, smilax, or of palmetto from the handle of a fan, 

 and compare them with your sketches of the cornstalk. 

 In which are the vascular fibers most abundant .'' Which 

 is the toughest and strongest .' Why t Trace the course 

 of the leaf fibers from the point of insertion to the 

 interior. How does it differ from that 

 of the fibers in a cornstalk .'' 



217. Growth of Monocotyledonous 

 Stems. — Refer to the experiment in Sec- 

 tion 43 ; refer also to what has just been 

 learned regarding the course of the leaf 

 veins at the nodes of the cornstalk (Sec. 

 213), and you will have no difificulty in 

 identifying these veins as part of the vas- 

 cular system. Each successive leaf sends 

 its vascular bundles down into the main 

 system of the stem, and any increase 

 297. — Longitudinal i" the diameter of monocotyledons takes 

 section through the place by the intercalation of new bundles 



stem of a palm, show- 

 ing the curved course from the Icavcs as they develop at the 

 of the fibrovascuiar nodes above. In jointed stems like the 



bundles (Gkay, after ' 



falkenberg). ■ corn and sugar cane and other grasses, 



