50 MONOCOTYLEDONE^E. 



Fig. 20. 



Section of a polyanthus narcissus after flowering : a, scape un<l 

 accompanying leaves; ft, 6, leaves of the succeeding divisions 

 which have not yet flowered. 



But there are various modifications of bulbs : the 

 leaves of Allium porrum*-, and Agapantlius umbel- 

 Idtus^, are but slightly incrassated at the base ; the 

 Allium Cepal is peculiar in having 1 cylindrical hollow 

 leaves ; consequently the tunics of the bulb are entire, 

 except a lateral slit through which each interior leaf 

 protrudes through the exterior one which involves it. 

 The gouty stems of the Pancratium and Crinum can 

 hardly be ranked as bulbs, because the protuberant 

 investment at the base is only the vestige of 

 former leaves, which have a permanent character for 

 the protection of the stem. 



Besides these differences, there is another remark- 

 able structure of the bulb which deserves the atten- 

 tion of physiologists. Some, as the tulip and hyacinth, 

 have their flowers terminal ; when these are expanded 



* Common leek. -j- Blue African lily. J Onion. 



