346 METHODS IN PLANT HISTOLOGY 



Gnetum thrives in the greenhouse, but the other two have not been 

 cultivated successfully. The wood of Ephedra and Gnetum is extreme- 

 ly hard, but can be cut by the hot steam method. The wood of Wel- 

 witschia consists, principally, of a delicate parenchyma tissue, with 

 numerous, large, rigid, spicular cells. Dr. Langdon cut beautiful sec- 

 tions by treating with 50 per cent hydrofluoric acid for 3-6 weeks and 

 imbedding in paraffin. There should be no haste. Allow 24 hours for 

 each grade of alcohol and for each grade of the paraffin mixtures. 

 Allow at least 24 hours for the xylol-paraffin mixtures, half of the time 

 at room temperature and half, on the top of the bath. Put the mate- 

 rial in an open dish in the bath. About 2 or 3 days will be required, 

 and the paraffin should be changed 3 or 4 times. 



All of the Gnetales show vessels in the secondary wood, an angio- 

 sperm character. 



The strobili can be fixed in formalin-acetic-alcohol, but in Ephedra 

 the dry chaffy scales must be dissected away before completing the 

 dehydration and infiltration with paraffin. If you can secure material 

 of Ephedra, Dr. Land's researches present a very complete life-history, 

 with dates of various stages and suggestions for fixing and staining. 



