134 Botanical Microtechnique 



sprengeri, an important j^lani in the florist trade, has a thin woody 

 stem. The younger portions near the tip can be cut in paraffin, the 

 old woody stems must be cut in celloidin. AVild species of Smilax have 

 a woody stem. Kill the woody stems of Asparagus and Smilax in FA A, 

 and cut in celloidin only if a sample embedded in paraffin cannot 

 be cut. 



DICOTYLEDONOUS AND CONIFEROUS STEMS 



The apical meristcmatic regions of dicot stems have been discussed 

 in the section on apical meristems. The tissue systems of these stems 

 differentiate very rapidly close to the apex, and the first few inter- 

 nodes below the terminal bud show the fully developed primary 

 tissues and the initiation of secondary activity. A convenient though 

 artificial and arbitrary classification of stem types is in common use. 

 Herbaceous stems develop comparatively little secondai7 wood, and, 

 if a complete cylinder of wood is produced, it is laid down late in the 

 growth period. Woody stems begin the formation of a complete 

 cylinder of secondary wood early in the season and produce an 

 extensive cylinder of highly lignified xylem. Every possible gradation 

 of woodiness between these two types may be found in the plants 

 about us. The following examples are recommended either because 

 they are of economic importance or because they present some 

 structural feattire of fundamental importance. 



Plants that can be grown quickly in pots are convenient subjects for 

 the herbaceous stem. Plants of kidney beans, peas, and soybeans attain 

 usable size in a short time. Actively growing field materials are the 

 best source for sweet clover, alsike clover, and alfalfa (Fig. 13.7) . Any 

 of these legume stems can be killed in Craf III. The softer internodes 

 can be carried through an accione-xylene or alcohol-xylcne series. 

 The harder stems, esiiecially soybean, cut better after dioxan or the 

 butyl alcohols (Fig. 13.6). 



The cultivated sunflower, Hclidiilhtis,, and Chrysanilirmtiiii are 

 good representatives of the Compositae. The common fleabane, 

 Erigeron, is a suitable native subject in iliis family. The above stems 

 seem to withstand the dehydrating action of FAA without marked 

 plasmolysis, and a strong Nawaschin modification like Craf I\' or V 

 is satisfactory. The butyl alcohol process is reconnninded for these 

 rather tough stems. 



Bicollateral bundles are characteristic of the Cucurbitaceae and 

 Solanaccae (Fig. 13.7). Important members of these families can be 

 obtained easily. Seedlings of scjuash, pumpkin, or melon grow rapidly 



