PROCEEDINQS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VI, pp. I-203. Sept. io, 1904. 



CONTRIBUTIONS TO THE KNOWLEDGE OF THE 



LIFE HISTORY OF PINUS WITH SPECIAL 



REFERENCE TO SPOROGENESIS, THE 



DEVELOPMENT OF THE GAMETO- 



PHYTES AND FERTILIZATION. 



By Margaret C. Ferguson, Ph.D., 

 Associate Professor of Botany, Wellesley Cot lege. 



Plates I-XXIV. v^ 



CONTENTS. 



Introduction. 



Purpose of the study 3 



Historical notes 5 



Methods. 



Collecting 12 



Fixing 13 



Staining. 15 



Chapter I. Microsporogenesis. 



The microsporangium. 



The wall of the pollen- sac '. 17 



The primitive archesporium 18 



Tetrad-division. 



The definitive archesporium 20 



The first nuclear division of the microspore-mother-cell 21 



The second mitosis of the mother-cell 30 



The problem of reduction 31 



Development of the microspore. 



The formation of the spore-wall 34 



The origin of the air-sacs and liljeration of the microspore .... 36 



The growth of the microspore 37 



Summary 39 



Proc. Wash. Acad. Sci., September, 1904. (i) 



