5IO General Botany 



The pine sporophyte. The vegetative sporophyte consists of 

 the root system, the stem and its branches, and the scales and 

 needle leaves. The stem, in cross-section, is quite similar to 

 that of a woody dicot. It differs chiefly in the absence of true 

 vessels or tracheae. 



Two kinds of cones, the staminate and ovulate, are produced on 

 the same tree. In them are formed the microspores and mega- 

 spores, within which the male and female gametophytes develop. 



The staminate cone. A cluster of staminate cones develops 

 in the spring at the base of the new stem segment. These cones 

 are small, short-lived structures, falling from the tree as soon as 

 the pollen is shed. Each cone is made up of yellow, membra- 

 nous sporophylls, each bearing two microsporangia (pollen sacs) 

 on its lower face. The pollen, or microspore, at first consists of 

 a single cell, but before it is shed cell division occurs and the 

 mature pollen grain consists of four cells. Two of these cells 

 soon degenerate. The third cell is called the generative cell; 

 and the fourth, which occupies most of the pollen grain, is called 

 the tube cell. The outer wall of the pollen grain also enlarges 

 and separates from the inner wall, forming on either side of the 

 living cells two miniature balloons which help support the 

 grain in the air. The four cells within the pollen represent the 

 remnants of a male gametophyte. 



In late spring the pollen sacs break open and the pollen is 

 blown about by the wind. The amount of pollen produced by 

 a pine forest is enormous, and when scattered may give the soil 

 and all near-by objects a yellow tinge as though powdered sulfur 

 had been sprinkled about. 



The ovulate cone. The megasporophylls are at first small, 

 green, fleshy scales, but ultimately they enlarge and become 

 woody. They develop on small lateral branches near the upper 

 end of the year's growth segment. There are usually two or 

 three of these ovulate cones formed near each other. 



Each sporophyll has two megasporangia or ovules on its upper 



