1302 



Yanijs iij)on liiriit porous soils iu areas where the rainfall is 

 relatively small may V)e left to trail their vines on the soil, for 

 thereby the moisture in it is retained: but nowhere in the Malay 

 Peninjsula is the rainfall small enough to justify this : on the other 

 hand the great room afforded for development by the use of stakes 

 produces a greatly increased return. Experiments, demonstrating 

 this increase, were performed twelve years ago in the island of St. 

 Lucia, West Indies (Agricultural Bulletin, Barbados, VIII, April 

 3rd, in09, p. 105). The results were as follows: — 



Race of Return when Return when 



Yam not Staked Staked 



"Lisbon" '^.2 tons per acre. 6.7 tons per acre. 



" Bottle-neck Lisbon " '2.4 tons per acre. 4.3 tons per acre. 



Since the al)0ve was written the following note has appeared 

 in the Agricultural News. March Gth, 1920. 



" A note in the iVgricultural News February 8th, 1919. drew 

 attention to an ex])erimeut conducted at the Botanic Station, Mont- 

 serrat, in yam cultivation, as to whether it was profitable or not to 

 provide stakes for the vines to run on. Mr. Eobson, the Curator, 

 came to the conclusion that the increased yield produced by the 

 staked plants would more than pay for the increased cost involved. 



" Mr. Eobson has recently forwarded a note upon a similar trial 

 carried out in 1919 with the results obtained therefrom, six roM'S of 

 six different varieties of yam were planted on ordinary banks, to 

 which pen manure had been supplied, 4 feet apart, the plants being 

 three feet apart in the row. These rows were staked, and five rows 

 unstaked were ])lanted alongside as a control. The yams were 

 planted on May 1st, 1919, and reaped on January 19, 1920. The 

 results showed that in every case there was a large increase in yield 

 from the staked rows as compared with the unstaked ones, amount- 

 ing to more than 100 per cent, on the total yield, thus confirming 

 the results obtained in 1918." 



I. H. BUKKILL. 



Some Factors in Plant Competition. 



A preliminary account of the results of experiments conducted 

 at the Eothamsted Experimental station to ascertain the relative 

 importance of the different factors that come into play when one 

 plant enters into competition with another is given in " The Annals 

 of Applied Biology ", Vol. YI, Nos. 2 and 3. 



" Competition of one plant with another is a very complex, not 

 a simple, phenomenon, and may be broadly analysed as follows: 



(1) Competition for food from the soil. 



(2) Competition for water. 



(3) Competition for light. 



(4) The possible harmful effect due to toxic excretions from 



the roots, if such occur. 

 " The first three factors lend themselves to direct experiment ; 

 the fourth is more difficult to demonstrate ])ut the possibility of its 

 existence must be reckoned with in estimating results." 



