504 
PHANEROGAMS. 
persistence, becoming lignified and often very hard. The numerous pollen-sacs on 
the under side of the stamens are usually collected into small groups numbering 
from two to five, like the sori of Ferns, these again forming larger groups on 
the right and left side of the leaf. The pollen-sacs are globular or ellipsoidal, 
usually about i mm. in size, and are attached with a narrow base to the under 
side of the stamen ; Karsten states that in Zamia spiralis they are even stalked. 
They dehisce longitudinally, and are in all respects much more like the sporangia 
Fig. 343.— a carpel of Cycas revoluta (reduced about k.)\f pinnae of the leaf-like carpel ; sk ovules replacing thd 
lower pinnae ; sk' an ovule further developed. 
of Ferns than the pollen-sacs of other Phanerogams, from which they also differ 
in the firmness and hardness of their wall. The mode of development of the 
pollen-sacs and pollen-grains of Cycadeae was till lately unknown ; it has only 
quite recendy been observed by Juranyi in Ceratozamia longifolia. The pollen- 
sacs are formed on the under side of the stamens in the form of small papillae, 
probably consisting from the first of several cells over which the epidermis of 
the surface of the leaf is continuous. The inner tissue is next differentiated 
