204 TEANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



altering in position as they are focussed. They are hence 

 readily distinguishable from true septa. 



The foregoing observations were made in the Botanical 

 Laboratory of University College, Liverpool. 



Explanation of Plate XI. 



Figs. 1 — 6, 10 — 19, Narcissus ; 7 — 9, Mercurialis ; 20, 

 Vaccinnim; 21, Cheiranthus. 



Fig. 1. Commencement of dichotomous branching. 



Fig. 2. ,, ,, lateral ,, 



Fig. 3. Later stage of 2. 



Fig. 4. Young plasmolysed pollen grains, shewing extru- 

 sion of starch grains. 



Fig. 5. Forms produced in dilute sugar solution. 



Figs. 7 — 9. Formation of normal and branched pollen tube. 



Fig. 10. Extrusion of zymogenic granules from apical pore. 



Fig. 11. Apex of same tube three hours later. 



Fig. 12. Apex of pollen tube which has just ruptured. 



Fig. 13. Swollen lamellated apex of pollen tube which has 

 ceased to elongate. 



Fig. 14. Apex of old pollen tube shewing globular dilata- 

 tion, formation of ingrowth and septum-like 

 crease. 



Fig. 15. Same pollen tube under low power. 



Fig. 16. Formation of septum along with turgidity of 

 basal portion of tube causing an attempt at 

 branching. 



Figs. 17 — 18. Commencing ingrowths. 



Fig. 19. Lamellation of wall and ingrowths, [^ im- 

 mersion] . 



Fig. 20. Formation of septa and thickening of wall. 



Fig. 21. Septa enclosing reproductive nucleus. 



