Z THE PROTOPLAST 



iiitiinato relationship existing between llie eell wall and the proto- 

 l)Ia.sm (luring eell differentiation, (2) by the very common occur- 

 rence of protoplasmic connections or plasmodesmuta which 

 penetrate the wall at various points, and (3) by the peculiar 

 behavior of the wall in certain algae (cf. Anderson 1935, pp. 

 71-72). ]\fany important cell types in vascular plants such as 

 fibers, tracheids, vessel elements, and sclereides consist only of 

 the wall at maturity. However, it is entirely appropriate to 

 designate them as "cells" since the loss of their jirotoplasts 

 occurs during the later stages of differentiation. 



II. The Cells of Plant Hairs. — The cells of many plant hairs 

 furnish very useful material for a study of the protoplast. Be- 

 cause such cells are usually highly vacuolated and hence semi- 

 transparent, they may be easily studied without special prepara- 

 tion or staining. Indeed, in the staminal hairs of Tnidcscantia, 

 the brilliantly colored cell sap in the vacuome provides a splendid 

 optical contrast for the gray cytoplasm and nucleus. 



Obtain a transverse section near the tij) of the stem of petunia 

 or squash, mount it carefully in water and examine the prepara- 

 tion under lov^ mugnification. A number of semi-transparent 

 hairs, variable in size and in the form of their terminal cells, 

 will be seen radiating from the edge of the section. Thin sec- 

 tions will show the mode of attachment of the base or "foot" of 

 the hair to the epidermis of the stem. Selecting an uninjured 

 and straight haii-, examine its component cells under hi<ih magni- 

 fication. Fre(|upntly the lower or basal cells of the hair will prove 

 most suitable I'oi- this study. Wy carefully regulating the light 

 and constantly using the fine adjustment on the microscope, the 

 nucleus, with its nucleolus will be visible. In color, the nucleiis 

 will aj)j)ear gray and slightly opaque. Often the nucleus may 

 appear to be imbedded in tlic thin layer of cutoplasni lining the 

 wall of the cell, ("onnnonly. however, the nucleus is suspended in 

 various positions by a delicate and complex network of cyto- 

 plasmic sfrauds which extend from the jieripheral cytoplasm 

 tlu'ough the clear watei-y cell-sap of the prominent vacuome of 

 the cell. In many of llic cells of the hair, small plasiids may be 

 seen in the pei-iphei-al cytoplasm and sometimes in the larger cyto- 

 plasmic strands. Well-mounted uninjured sections which have 



