432 piper: new leguminosae 



thermostat, for which SHgh has given an equation. From this 

 equation it follows that the length of stroke usually employed, 

 20 or more times the backlash, makes the variation from day 

 to day much greater than in the previously discussed type. It 

 also follows, however, that the error can be diminished by short- 

 ening the stroke, by using an excess of heating power, and by 

 enlarging the bulb. How far these expedients can be carried 

 without introducing irregularity of action has not yet been 

 worked out. 



A third means for increasing precision is to put the heater 

 very near the regulator bulb. This is like the Gouy regulator 

 in making the oscillations of the heating current so rapid and 

 small that the oscillations of the bath become negligible. It is 

 well known, and is often hailed as a complete solution of the 

 problem of temperature regulation. What is not nearly so 

 well known is that this method is also like the Gouy in giving 

 relatively large variations from day to day. This is because 

 the bulb is intermittently bathed in water considerably warmer 

 than the rest of the bath. Hence as the amount of heat re- 

 quired varies, the relative temperature of bulb and bath, and 

 therefore, the absolute temperature of the bath, varies also. 



BOTANY. — A new genus of Leguminosae. C. V. Piper, Bureau 

 of Plant Industry.^ 



In a study of the genus Canavalia, to which the cultivated jack 

 bean and sword bean belong, it has become evident that the 

 generic characters will need some revision. Among the speci- 

 mens referred to this genus in the U. S. National Herbarium was 

 found the new species herewith described, diverging so much 

 from any other as to necessitate the proposal of a new genus 

 for its reception. Superficially, it has much resemblance to 

 Canavalia, but the floral characters indicate that its relationship 

 is much closer to Dolichos. 



Monoplegma, gen. nov. » 



Leaves palmately trifoliolate ; leaflets entire, 3 -nerved from the base 

 the two lateral nerves nearly as large as the midrib ; flowers in racemes, 

 ' Received July 21, 1920. 



