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 revoliUa (reduced about h.)\/ piimse of the leaf-like carpel ; sk ovules replacing the" 

 lower pinnce ; 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 recently been observed by Juranyi in Ceratozamia longt/olia. 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 

 ths surface of the leaf is continuous. The inner tissue is next differentiated 



