268 Methods in Plant Histology 



dissect out the desirable parts. In the common sunflower, Helian- 

 thus annuus, the young floral parts, like the mature head, are so very 

 large that a satisfactory study may be made with a low-power 

 objective. As in case of the thistle, the involucre must be trimmed 

 away and only enough of the receptacle retained to hold the florets 

 together. 



Spermatogenesis. The earlier stages in spermatogenesis will 

 be found in the preparations of floral development. The origin of 

 the archesporium, the origin of sporogenous tissue, and the formation 

 of the tapetum are beautifully shown in longitudinal and in transverse 

 sections of the anthers of Taraxacum and many other Compositae. 

 Transverse sections of the head of Taraxacum or any similiar head 

 at the time when pollen mother cells are rounding off in the center of 

 the head, will show various stages from the mother cells in the center 

 to the tetrads of spores at the periphery. Transverse sections of 

 the anther of Polygala give exceptionally well-defined views of the 

 archesporial cells and sporogenous areas. 



Lilium, Trillium, Galtonia, Iris, Tradescantia, Vicia, and Podo- 

 phyllum can be recommended for demonstrating the nuclear changes 

 involved in the formation of spores from the mother cell (Fig. 94). 

 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 

 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 Iris 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 mother cells 



