417 



A few filaments observed Nov. 23, 1909, Jan. 9, 1910. Never observed 

 in fruit. 

 Oedogonium nndulatuin Brebisson. 



The most abundant alga in the pond. It is present throughout the 

 year. It was observed fruiting sexually on Nov. 16, 1909, and April 13. 

 1910. After the sexual season in the spring the plants decline in vigor. 

 There are enormous numbers of oospores present in the water at this 

 time. 

 Chaetophora pisiformis Roth. 



Common at all seasons on stems. 



Typha latifolia L. 



This is the most conspicuous plant m the pond. It covered the shal- 

 lower two-thirds of the pond in 1908 and has since increased to about three- 

 fourths of the total area. It is from this plant that most of the vegetable 

 debris on the bottom of the pond is derived. 



In 1910 shoots appeared from the stolons ^Nlar. 24. Seeds began ger- 

 minating April 8. flowers were formed in June and seeds were ripe early in 

 September. 



The st-eds which fall in the water are usually blown to the lee side 

 of the pond where tliey collect in dense masses. This results in very 

 weak seedlings during germination. A slight reduction of level is fatal 

 at this period. Besides this, the margin where these seeds germinate is 

 already occupied by parent plants. From these facts, it is evident that the 

 seeds of Typha are very inefficient in increasing the number of plants in 

 a pond where it is already established. The increase is derived chiefly 

 from buds from the stolons. The seeds, while ill adapted to this function, 

 are very efficient in securing the introduction of the species into ponds 

 unoccupied by it. On a spike 150 mm. long, I have estimated the number 

 of seeds to be 27,000. How far they may be carried by wind is conjectural, 

 and on that account this efficiency can not be reduced to figures. The 

 chances of introduction of any wind-blown seed is inverse to the distance 

 from the center of distribution, but the proportion is unknown. Certainly 

 it is greater in the direction of the prevailing winds than in any other. It 

 may be observed that if the seeds were distributed eA'enly over a circle 

 whose radius is one mil" (the distance to the nearest pond) a seed from 

 each spike would have approximately five chances in six of hitting a pond 

 of that size (70 ft. in diameter) placed anywhere in this cii*cle. 



[27—26988] 



