Collecting and Subdividing Plant Materials 9 



it is desirable to cut the organ being studied into the smallest pieces 

 that will show the necessary relationship of parts. 



The subdividing of soft fresh material is best done with a razor 

 blade, with the material placed on a sheet of wet blotting paper or 

 held carefully against a finger. Excessive pressure against the support 

 is likelv to ruj)ture delicate tissues as in the mesophyll of leaves 

 (Fig. 11.1) or the chlorenchyma of a stem (Fig. 11.2). Such damage 

 does not become visible until the sections in the ribbon are examined 

 or possibly not until the finished slide is examined. The usual results 

 are peeling of the epidermis and distortion of the crushed tissues. 



Leaves are almost invariably cut into small pieces for processing. 

 Narrow leaves that are not much over 5 mm. wide, may be cut into 

 complete transverse pieces measiuing 2 to 4 mm. along the rib (Fig. 

 2.\ A-D) . Examples of this type are bluegrass, garden pinks, hedge 

 mustard, and some narrow-leaved milkweeds. Broad leaves should be 

 cut into small pieces, selected to include midrib, lateral veins, fungus 

 pustules, fern sori, or other desired structures (Fig. 2.1 F, G, I, J) . 

 The enlarged views of the pieces of leaf (Fig. 2.1 B, D, G, I, J) and 

 the pieces of embedded tissue mounted on blocks ready for sectioning 

 {E and K) will aid in visualizing the orientation of pieces. Particular 

 care should be used in subdividing pathological material (Fig. 2.1 /, 

 /) . If it is necessary to know which is the long axis of the leaf, cut 

 all pieces so that the shorter dimension is along the long axis of the 

 leaf, or vice versa, and record the method in yoin- notes. 



Herbaceous stems, roots, petioles, and other more or less cylin- 

 drical organs are usually cut into short sections or disks. When cut- 

 ting out sections or subdividing pieces, do not roll or press the pieces. 

 Keep the material moist, and work rapidly. After the final subdivision, 

 drop the pieces into the killing fluid promptly. By means of descrip- 

 tions and sketches, like those in Figs. 2.1 and 2.2, keep an accurate 

 record of the part of the plant from which the pieces of tissue were 

 obtained. 



Figure 2.2 gives additional suggestions for subdividing organs. A 

 stem that does not exceed 2 mm. in diameter should be cut into 

 sections 2 mm. long if highly cutinized, but may be as long as 10 

 mm. if the surface is permeable. An organ 5 mm. in diameter should 

 be cut into 5-mm. lengths. An organ 1 cm. in diameter should be 

 cut into disks 2 to 5 mm. thick. Stems of larger diameter are usually 

 cut into 5-mm. disks that are halved or cjuartered longitudinally or 

 di\ided into wedge-shaped pieces. 



