724 Beer— Studies in Spore Development . II. 
prophase, so also is there no hard and fast line which is invariably fol- 
lowed by the chromosomes in the dispersal of their substance at the telo- 
phase. 
11. There are two types of pollen- wall in the Compositae. All the 
Tubuliflorae which have been examined possess pollen-grains with an un- 
folded exine, whilst the exospore of all the Liguliflorae observed is thrown 
into a number of distinct folds. The details of the structure of the pollen- 
membrane is reserved for a separate part of these £ Studies 
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20 . 
