Vegetative Organs of Vascular Plants 147 



sent the broad flat type. The extremely large stomates are the standard 

 subject for studying sectional views of the stomatc. Kill in Craf II 

 and process by the alcohol-xylene method. The thinness of the cell 

 walls necessitates a contrasting wall stain like hemalum. The stomates 

 are showm with almost diagrammatic clarity. Leaves of Zebrina, 

 Rhoeo, Tradescantia, Polygonatuni hiflonim, and Smilacina race- 

 mosa can be prepared by the above method. 



The tender, cylindrical, hollow leaf of onion is preserved in 

 excellent condition in Craf I and processed like those of lily. 



The touoh leaf of Iris is difficult to section. Fair cellular fixation 

 can be obtained with FAA and excellent preservation with Craf I 

 if the pieces are very narrow. The TBA process minimizes brittleness 

 in paraffin. 



The favorite subjects for the study of coniferous leaves are Pimis 

 strobus, a soft pine, and P. laricio austriaca, P. sylvestris, or other 

 hard pine. Needles collected in the late fall and in winter are very 

 hard and become extremely brittle in the paraffin. The cells contain 

 much granular resinous material which remains in the finished prepa- 

 ration. In July the needles are full grown, with all structural features 

 fully developed, but they are still sufficiently soft to cut readily, and 

 do not have excessive deposits in the cells. Kill in Craf III, and pro- 

 cess in TBA; safranin-fast green yields a beautiful preparation. 

 Longitudinal as w^ell as cross sections should be made. Needles of 

 the spruces (Picea) are also in the tough, wiry category and should 

 be processed like those of pine. 



The flat type of needle is represented by Douglas fir {Pseudotsuga 

 taxi f olio) , the hemlock (Tsuga) , or the fir (Abies). These may be 

 killed in the fluids recommended above. Although these relatively 

 soft needles can be processed through xylene, dioxan and butyl alco- 

 hol improve the cutting properties. 



The broad leaf of Ginkgo biloba should not be omitted from a 

 study of the gymnosperm leaf. Collect leaves in July, and kill in Craf 

 III. 



The leaves of cycads are difficult subjects because of their tough, 

 xerophytic features. Select pinnules that are not fully matured and 

 toughened. Cut transversely into narrow pieces and kill in FAA. The 

 nonalcoholic fluids penetrate poorly, but excellent fixation in small 

 pieces is obtained with Craf II. Xylene renders the tissues very brittle, 

 but tertiary butyl alcohol permits satisfactory sectioning. 



Fern leaves are readily obtainable from the common Boston fern. 

 Use pinnules that have expanded to maximum size but are still bright. 



