Fink : CONTRIBUTION TO THE LIFE-HISTORY OF RUMEX. 151 



lowed by methyl blue was found to be the best stain for stages 

 before the establishment of the macrospore, and safranin or Del- 

 afield's hasmatoxylin gave best results from this period up to the 

 fecundation of the .egg, after which the hasmatoxylin proved 

 best. 



The nucellus of Polygonwn ereclum is transparent enough to 

 show the nuclei of various stages of development of the sac, ex- 

 cept the antipodals, as well as the cytoplasm and vacuoles with 

 oil immersion lens, without sectioning or any treatment what- 

 ever. The results, however, were not reliable enough for my 

 purpose, nor are they certain enough for use in instruction. 



The figures are all drawn to the same scale by using one-inch 

 Leitz eye piece, one and one-half-inch Leitz objective and 

 camera lucida. 



EXPLANATION OF PLATES. 



NOTE. All figures are of Rumex verticillatus unless otherwise 

 indicated. The figures of the first two plates are reduced to one-half 

 the original size of drawings, those of the last two to one-third. 



Plate IX. 



1 . Upper portion of nucellus showing the archesporium. 



2. Later stage showing the primary tapetum cut off above and the 

 mother cell of the embryo sac below. 



3. The tapetum has divided into two tapetal cells and the mother 

 cell has increased considerably in size. 



4. Stage between 2 and 3 showing the tapetum dividing. 



5. Four tapetal cells and the elongated mother cell. 



6. The mother cell dividing and one tapetal cell above. 



7. The four potential macrospores derived from the mother cell. 



8. The macrospore and a highly refractive cytoplasmic cap, repre- 

 senting an almost completely absorbed cell, either a tapetal cell or the 

 upper one of the potential macrospores. 



9. The nucleus of the macrospore dividing. 



10. A somewhat older stage than 7 and showing the upper three 

 potential macrospores partly absorbed by the lowest one, which is to 

 become the macrospore. 



1 1 . Embryo sac containing two nuclei resulting from the division of 

 the nucleus of the macrospore, the lower one being somewhat larger. 

 The highly refractive remains of four nearly absorbed cells of the nu- 

 cellus are also shown. 



