1 



104 DuGGAR : Development oe the Pollen Grain 



i6 c.c. \^<> Chromic acid "] i^ grams 



3 c.c. 2^ Osmic acid ( ^ y> grams 



I c.c. Glacial acetic acid 



Water^ about 



The Flcmming triple stain of safranin, gentian violet, and orange 

 was used to some extent. After much experimentation, however, 

 it was found advisable to leave out the safranin. Gentian of tlie 

 full strength recommended gave good results in chromosome dif- 

 ferentiation ; but the spindle structures were not then well stfiined. 

 For spindle structures, and for the differentiation of the kino- 

 plasm, best results were obtained by the use of a very weak gen- 

 • tian, in which the sections were stained from twelve to twenty-four 

 hours. 



Hxplanatiou of Plates. 



Plate 352. 



All figures were drawn with the aid of an Abbe camera lucida, projection 30 cm., 



tube length 15.5 cm., Leitz oculars 3 and S, and objectives 7 and ^^ (horn. imm. ) were 

 used. 



Fig. I. Cross section of young anther showing early differentiation of peribleni 

 layer, from which the archcsporium and wall layers are eventually derived. 



Fig. 2. The four sporangial regions well differentiated; later than Fig. I. 



Fig. 3. Outline of mature anthers in cross section. 



Fig. 4. Division of the hypodermal layer forming primitive archcsporium within. 



Figs. 5 and 6. Formation of the first true wall layer without, and the outer tapctum 

 within. 



Fig. 7. Development of the two wall layers. 



Fig. 8. Extra growth around the ends of the archcsporial regions. 



Fig, 9. Nuclear division in the tapetid cells. 



Fig. 10. Increase in extent of the archcsporial layer by anticlinal divisions of the 

 vegetative type. 



Fig. II. Epidermis and wall layers at the maturity of the anthers. 

 Fig. 12. Differentiation of the hypodermal cell as the initial cell of the macro- 

 sporic archcsporium. 



Fig. 13. Growth of the archesporium and development of the integument. 

 Fig. 14. Archesporial cell immediately preceding the first division. 



Platk 353. 



Fig. 15. Second division in the axial row. 



Fig. 16. The four cells of the axial row. 



Fig. 17. Development of the fourth cell in the axial row at the expense of the 



others. 



Fig. iS. Developing eml>ryo-sac with two small nuclei. 



Fig. 19. Mature embryo-sac with syncrgids and egg-cell, fusing polar nuclei, and 

 antipodals. 



