SUGGESTED DRAWINGS AND NOTES 15 



a pair of bordered pits) are crossed. Furthermore, each slit- 

 shaped aperture is connected with the pit cavity by a channel hav- 

 ing the form of a flattened funnel (cf. Eames and MacDaniels, 

 1925, p. 33, Figs. 21-22). The vestigial pit-pairs of bast fibers 

 are frequently less complex, and consist of small circular aper- 

 tures and very narrow tubular cavities. Such pits are often 

 regarded morphologically as specialized simple pits. 



Ohtain a preparation of macerated secondary xylem of the 

 sycamore (Platanus) and examine it under low magnification, 

 noting the numerous long, acuminate wood fibers. Careful study 

 of these fibers under high magnification will reveal the character- 

 istic arrangement of tlie vestigial pits with their narrow apertures 

 and inconspicuous "halo-like" cavities. Occasional fibers may 

 be turned in such a way that the vestigial pits or pit-pairs may be 

 visible in sectional view. A study should also be made of pit 

 structure as revealed in prepared and stained longisections 

 through the xylem. 



Make a comparative study of the vestigial pit-pairs of the bast 

 fibers of Tilia or Platanus with the use of macerated as well as 

 stained and sectioned material. 



V. Suggested Drawings and Notes. — 



1. Prepare drawings showing the arrangement and approxi- 

 mate number of plasmoclesmata in a small group of connected 

 endosperm cells of Diospyros. Briefl}- summarize the possible 

 importance of the presence of plasmodesmata with reference to 

 the trans-location of organic materials in plants. 



2. Draw a group of pith or cortical parenchyma cells from 

 the stem section of Tilia or Pelargonium showing and labeling 

 the following: compound middle lamella, protoplast, intercellular 

 air spaces. In what kinds of plant tissue are intercellular air 

 spaces likely to be most prominent ? Explain, from a physio- 

 logical viewpoint (cf. Ilaberlandt, Ch. IX). 



3. Draw a group of bast fibers of Tilia as seen in the trans- 

 section of the stem, showing and labeling the foHowing: com- 

 pound middle lamella, secondary wall, and lumen. What might 

 be the "cause" of the deeply-stained thickenings frequently vis- 

 ible at the common point of contact between several bast fibers? 



