SPERMATOPHYTES—ANGIOSPERMS 
299 
involved in the formation of spores from the mother-cell (Fig. 106). 
Several species of Lilium are common in greenhouses, and these 
may be used where wild material is not available. In early stages, 
where the sporogenous cells have not yet begun to round off into spore 
mother-cells, it is sufficient to remove the perianth, retaining just 
enough of the receptacle to hold the stamens in place. Transverse 
sections show the six stamens and also the young ovary. After the 
Fig. 106 .—Lilium candidum: photomicrograph of mitosis in pollen mother-cells; in one of 
the pollen mother-cells the twelve chromosomes can be counted; from a preparation by F. L. 
Pickett. Negative by Miss Ethel Thomas. X260. 
spore mother-cells have begun to round off,- each stamen should be 
removed so as to be cut separately. In securing the desirable stages 
showing the division of the mother-cell into microspores, much time 
and patience will be saved by determining the stage of development 
before fixing the material. Mitosis is more or less simultaneous 
throughout an anther. Long anthers are particularly favorable, 
since they may show a very closely graded series of the various 
phases of mitosis. An anther of Lilium may show mother-cells with 
nuclei in synapsis at the top, while the mother-cells at the bottom 
have reached the equatorial plate stage of the first division; or, the 
