CONIFERALES 307 



from the inline. A study of very thin sections of Pinus and Abies, 

 sharply stained with safranin and light green, supports Dr. Fergu- 

 son's conclusion. Only about one-third of the genera have wings or 

 bladders of any sort, the great majority having no such develop- 

 ments of the exine. When wings are present, there are generally two, 

 as in Pinus; but Microcachrys has three, and sometimes four, or even 

 five or six. Most species of Podocarpus have two large wings, but 

 P. dacrydioides has three. Pherosphaera has very small pollen grains 

 with three wings. 



The male gametophyte is in various stages of development when 

 the pollen is shed, but for any given species in any given locality the 

 time of shedding will vary little, and the stage of development may 

 not vary at all. 



Very few species, like Taxus canadensis and Cunninghamia sinen- 

 sis, shed the pollen in the uninucleate stage, and these will not have 

 any prothalHal cells. The first mitosis, after reaching the nucellus, 

 will be the one which gives rise to the generative cell and tube cell. 

 In species which have prothallial cells, these and the generative cell 

 are formed before the pollen is shed. 



Pinus is a familiar form with winged pollen and prothallial cells 

 (fig. 311). The figure begins with the second reduction division (A), 

 the tetrahedral arrangement of microspores is shown in B, and the 

 beginning of the wings in C. The first mitosis of the young gameto- 

 phyte is shown in D-F, in F, with the nucleus of the first prothaUial 

 cell already degenerating. G and H show the prophase and telophase 

 of the second mitosis, and /, the two prothalHal cells. These are usual- 

 ly overgrown by the vigorous intine before the third mitosis (/) , which 

 gives rise to the generative cell and tube cell, is completed. When 

 the two prothallial cells and the generative cell (K) have been 

 formed, the pollen is ready to be shed. In Pinus the succeeding 

 stages are found after the pollen has reached the nucellus of the 

 ovule (L). 



This is a very prevalent course of development of the male 

 gametophyte in conifers. Some differ in having no prothallial cells; 

 some, in having a greater display of prothallial cells; others differ in 

 the extent of development of the male gametophyte when the pollen 



