246 



Methods in Plant Histology 



The leaves.- -The young tender leaves should be fixed in formalin 

 alcohol and imbedded in paraffin. The adult leaves are rigid and 

 cut well freehand. . Stain sharply in safranin, extract the stain until 

 it almost entirely disappears from the cellulose walls, then stain in 

 light green. 



Spermatogenesis. Except in the earliest stages, the staminate 

 cones are too large to be cut whole. The individual sporophylls, 



FIG. 85. Ceratozamia mexicana: A, pollen grain which has been in a sugar solution 

 for two days; X876; B, nucellus with numerous pollen tubes; X17; C, basal end cf 

 pollen tube showing the persistent prothallial cell; outside it the stalk cell; and, above, 

 the two sperms still inclosed in the sperm mother cells; X156. 



with their sporangia, cut easily up to the formation of microspores; 

 then the sporangium wall hardens rapidly and cutting becomes 

 difficult. Up to the young microspore stage, fix in chromo-acetic 

 acid; fix later stages in formalin alcohol. Transverse sections are 

 more instructive and are much more easily cut, since the peripheral 

 end of the sphorophyll can be cut only in younger stages. 



