422 



STRUCTURE AND LIFE HISTORIES 



duced, consisting usually, in the white pine, of only four 

 cells, all in the same plane; the number of these cells is 

 somewhat variable. No neck-canal cells are formed; only 

 the egg, and the ventral canal-cell (the sister-cell of the 

 egg) which disorganizes early (Fig. 312). 



Fig. 312. — White pine {Pinns Strohus). \'ertical section through tlie 

 upper part of an ovule, shortly before fertilization, s.n, sperm-nuclei; 

 st.c, stalk-cell; t.n, tube-nucleus; arch, archegonium; e.n, egg-nucleus. 

 (After Margaret C. Ferguson.) 



374. Male Gametophyte. — The germination of the 

 microspore consists chiefly of a series of cell-divisions, all 

 within the wall of the microspore. The first three 

 divisions result in the formation of four cells, namely, two 

 prothallial cells, one mother-cell of the antheridium, and a 



