STRUCTURE AND DEVELOPMENT. 61 



whose exterior membranes are reticulate, tuberculate 

 or wholly smooth. Both coloured membranes are of 

 a compound character, consisting of a series of 

 infinitely thin layers. This is usually only apparent 

 in cases where the membrane happens to show a 

 ragged edge. Such ragged edge will often exhibit 

 from two up to twelve, or fifteen, layers. 



Below the second coloured membrane 



lies a third, clear, translucent and quite 

 membrane. . 



colourless, having the appearance or a 

 piece of fine glass. It has no rigidity of texture, but 

 when removed from the inner coloured membrane 

 spreads flat and limpid on the slide. 



On the removal of the third membrane 



traces of a fourth are found, re present- 

 membrane. . . . 



ing remains or the original wall or the 



oosphere. This membrane apparently becomes ulti- 

 mately absorbed and disappears. 



In many species oogonia may be ob- 

 served in which the spiral lines are still 

 conspicuous, but the whole surface presents a shell- 

 or porcelain-like appearance, often exhibiting a 

 metallic sheen. An examination of these fruits 

 shows that they possess the usual thin tough surface 

 cuticle of the spiral cells, but that a fine deposit of lime 

 has been secreted within the spiral-cells forming a hard 

 semi-transparent shell incasing the oospore. 



In almost every plant of every species 



bnorma OOS r nia are found in which no coloured 

 forms of fruit. Al 



oospore occurs, the transparent envelop- 

 ing cells clasping the naked colourless oosphere which 

 is often large and distended. If, as is conjectured, the 

 coloured membrane follows as a consequence of fertili- 

 zation, this condition may be due to non-fertilization. 



