96 



About the time the pileus begins to form the plant begins to 

 widen out. Up to this time, the increase by growth had been almost 

 entirely in length. In the increase in width, we find considerable 

 variation, more so than in the increase in length. But the average 

 of a number of plants shows that the lateral growth is but very 

 little faster than the terminal growth. In the increase in width, 

 there are of course two growing zones, both sides adding an 

 equal amount of tissue. Consequently the growth on one side is 

 but slightly over one half what it is on the terminal margin. As 

 a result, the hymenial surface of the mature plant is generally but 

 slightly wider than it is long. Of course, we sometimes find very 

 wide plants but these are quite often due to the fusing together 

 of several small caps that started from the same stalk. Curve C 

 in Figure 2 is plotted showing the increase in width, the values 

 being obtained from the average growth of a number of individ- 

 uals. The curve brings out the facts above mentioned. It is 

 strikingly similar to the one showing increase in length of the 

 pileus. Yet we have two sides increasing in width to only one 

 increasing in length. 



In conclusion, we will merely enumerate the results already 

 mentioned : ( i) Polyporus lucidns is a fast growing member of the 

 Polyporaceae, growth averaging about one half-centimeter per 

 day for the growing period. (2) Growth is exogenous, taking 

 place entirely at the edge of the plant and continuing as long as 

 conditions are favorable. (3) The change in the development 

 from stalk to pileus is a gradual process. (4) The average lateral 

 growth is but slightly more than the terminal growth. 



In closing, I wish to acknowledge my indebtedness to Pro- 

 fessor Atkinson, at whose suggestion this work was undertaken 

 and carried out. 



References to Literature in the Text 



1. Atkinson, George F. The Development of ..^^(^nW/'jr (frt7/z/^i-- 



tris Bot. Gaz. 42: 241-264. O 1906. 



2. Douglas, Gertrude E. Growth of Panaeolus retirngis. Tor- 



reya 6 : 157-165. 1906. 



3. Fries, E. Syst. Orb. Veg. i : 40. 



