40 LABORArollY S'lCDfKS ()/.' 77//v STEM 



What i.s its Position '' 



These are tlie questions to be kept in mind in tlie fol- 

 liiwing exereise. 



EXEIICISE XVIT. 1'lIK C'lIAUACTKRISTIC I'^EAIU II KS OF StEMS 



Red Maple. — t'.xuinine with care all marks and leatures iif fcivm 

 anil tlie [lositinii ol the In-aiielies ami Innls with ri'.s]iret to certain ol 

 tliesf niarlcings. Exaniiiii' especially the in'west jiarts, A kiw [lOWer 

 of the hand lens brinys out the desired puints well. 



Host trees and shrulis upon the appruacii of cold weather shiidd the 

 tender extreuLities of their stems hy mimerons scales. When yrowth 

 is resumed at the beginning of the next season, the scales fall away, 

 leaving scars to mark the occurrence of w inti-r. I'hese are to be looked 

 for on the material in hand, and noted as interesting traces of events 

 in the recent history of the twigs. But such annual deniarkations ai'e 

 not to be found on all stems. Refer to the ipiestions immediately pre- 

 ceding this exercise, and answer them in ihe notes. The sections of 

 the stem at which leaves are borne are called do/ts; the lengtlis 

 between leaves are inlernoiles. 



Draw the terminal, and one or tw"o adjacent, annual lengths of the 

 twig — enough to show all the points learned in the study. 



E.KERCisE XVIII. The Ixteuxal SxitucTriM: of Stems' 



Looking at the plants of the fields about us, we perceive the great- 

 est variety in the size, propoitions. and attitude of stems. In some 

 the stem is so short as to seem to be quite wanting, the leaves appear- 

 ing to spring directly from tlin loot. In other cases the stem, elon- 

 gated, reclines upon the yroniid. or Iwiin'S for supjiort upon any object 

 within reach. 



Yet thei'e is a prevailing type. Its erect haliit and height most 

 clearly show" the pmrpose of stems in general. AVliat is this pur- 

 pose '.' 



As lieight from the ground, means encounter with winds, the tall 

 stem must also be strong. Fui-thermore. the sap has a considerable 

 distance to travel from the root to the leafy crown, ami lience 

 the comluctioii of water becomes one of the functions of the stem. 



1 See also Chaiitnr X\'II. If coin|iound niierriscopes are availalile, the 

 mimite structure may be taken up more in di-tail tliaii the ilin-i-l ions here 

 given I'cquire. In any case use should here bi' made of figures and ex- 

 planations from Chapter XVII. Tlie cambium region, especiiUly, should 

 be located even under the dissecting microscope, and its meaning 

 explained. 



