Mar. II, 1918 Sterility in the Strawberry 643 



degree of abortion, as it is very common for practically all of the achenes 

 to develop on perfectly formed strawberries. 



The material was prepared for microscopic examination according 

 to the ordinary cytological methods. Carnoy's, Flemming's strong, 

 medium, and weak, and chromacetic-acid fixing solutions were used. 

 All g'ave very good results, except Carnoy's fluid. Sections were cut 

 from 4 to 20 ^t thick, the best results being obtained from those 4 to 6 /i 

 thick. The triple stain and Haidenhain's iron-alum-hymatoxylin stains 

 were used, both giving good satisfaction. 



The drawings in Plates B to E were outlined w^th the help of an Abbe 

 camera lucida. All, with a few exceptions noted, are drawn to the same 

 scale, in order that comparisons of cell size and cytoplasm content may be 

 readily made. 



Anther tissues. — The walls of the young anthers are made up of 

 four oblong layers of cells of about equal size ; the outer epidermal layer 

 and three inner layers. Inside of these layers there is usually one 

 layer of tapetal cells and about five layers of pollen mother cells, both 

 of which at this time are easily distinguished from the wall cells by 

 their large size and different staining reaction. 



The growth and development of the wall layers should be followed 

 because of its relation to the increase in size of the pollen mother-cell 

 cavity during the formation of the tetrads. As the pollen mother cells 

 prepare for reduction, and during the division, rapid cell division is tak- 

 ing place in the parietal cells, so that by the time the heterotypic division 

 is complete there is an appreciable increase in the size of the anther 

 cavity. Gradually the two inner layers of cells flatten out, owing prob- 

 ably to the growth of the outer layer, the cells of which rapidly increase 

 in size, although showing no further cell divisions. 



At the tetrad stage the inner layer is very much flattened, while the 

 middle layer is still plainly visible and the cells are still full of cytoplasm. 

 The cells of the outer layer are now very appreciably larger than the 

 epidermal cells, which have also grown slightly. After the liberation 

 of the microspores and while they are increasing in size, the epidermal 

 cells sometimes collapse, as their contents have become scant. By the 

 tirhe the microspores have nearly completed their growth and have 

 begun to divide, the cells of the outer layer have become deeper than 

 long and are nearly as large as the tapetal cells. At this time they show 

 distinctly the spiral thickenings which have to do with dehiscence. Both 

 of the inner layers have now collapsed or show very scant cytoplasm. 

 Before dehiscence the walls separating the members of the two pairs of 

 loculi break down, leaving two large loculi in each anther. The relation 

 between the increase in size of the anther cavities both during prepara- 

 tion for the first meiotic division and subsequent to it, and a diff'erence 

 which Fragaria spp. shows from some other forms in the history of the 

 mother-cell wall will be pointed out later. 



