278 CALIFORNIA ACADEMY OF SCIENCES. LPROC. 3D Ser. 



EXPLANATION OF PLATE XXV. 



The material was fixed in the field with Flemming's strong mixture; sec- 

 tions were cut 1-5 /x thick and stained with Flemming's triple stain. Figures 

 were drawn with the aid of the Abb6 camera lucida, Zeiss' Apoc. Hom. Im. 

 Obj. 2.00 mm., Comp. Oc. 8. All pertain to the division of the pollen- 

 mother-cells of Agave americana L. 



The lithographic plates reproduce the details of colour and form of the 

 preparations with great fidelity; the diflTerentiation of the kinoplasmic 

 elements is in no way exaggerated. 



Pollen-mother-cell before the beginning of spindle formation. The 

 cytoplasm shows the characteristic radial arrangement, the inner 

 portion being denser. 

 Progenetic layer in process of transition to the genetic (spindle 

 forming) stage. It shows violet granules along its periphery, and 

 outside this a few delicate fibres which later develop into the 

 exterior fibres. 

 The periphery of the layer more violet; exterior fibres more 



developed. 

 Periphery of the layer shows violet granules more closely crowded 

 together; radial genetic fibres appear within the layer; exterior 

 fibres still more developed; beginning of genetic stage. 

 Fig. 5. Spindle wall definitely formed; genetic and exterior fibres still more 



developed. 

 Fig. 6. Genetic layer widening; exterior fibres begin to form fibre cones. 

 Fig. 7. Beginning of cone formation. 

 Fig. 8. Further development of the spindle cones. 



