ODOURS OF PLANTS. 



807 



falls downwards on the approach of evening. This move- 

 ment is clearly analogous to the sleep of plants previously 

 described. ■ The lateral leaflets, 6, exhibit a constant movement 

 during the heat of the day, advancing by their edges towards the 

 large terminal leaflet and then „. 



retreating towards the base of ^3- '• 



the common petiole. This 

 movement takes place first on 

 one side and then on the other, 

 so that the point of each leaflet 

 describes a circle. The move- 

 ments resemble those of the 

 arms of the old semaphore tele- 

 graphs, and hence this plant 

 has been termed the Telegraph 

 plant. They go on to a less 

 extent even in the dark, and 

 are most evident when the 

 plants are in a vigorous state 

 of growth, and when exposed 

 to a high temperature. No 

 satisfactory explanation has as 

 yet been given of the direct 

 cause of this movement. 



h. Not periodical. — These ^^O- 1127. a portion of a branch, with a 

 , ■' • , 1 leal of Besmodiain gurajis. The leaf 



movements occur m the re- consists of a large terminal leatlet, a, 

 productive organs of a large andtwosmalleroues,?;. There are two 

 1 J? ii- -nu • other rudimentary leaflets, marked 



number of the Phanerogamia. also b, near the terminal leaflet. 

 The stamens sometimes curve 



inwards separately towards the stigma, as in Bicta graveolens 

 {fig. 597), and Parnassia pahistris; or in pairs, as in Saxifraga 

 tridactylites. They afterwards commonly return as nearly as 

 possible to their former position. In Farnassia the arrange- 

 ment appears to be one adapted, as the anthers are extrorse, to 

 prevent self-fertilization (see p. 779). In Passiflora, Nigella 

 sativa, certain Onagracese and Cactacese, &c., the styles move to 

 the stamens ; while in other Onagracese and certain Malvaceae, 

 &c., both stjdes and stamens move towards each other. No ex- 

 planation of a satisfactory nature has been given of the cause 

 of these movements, but their object is doubtless to assist in the 

 process of fertilization. 



5. Odours of Plants. — These are very various in kind, man^ 

 being highly agreeable, others excessively offensive, whilst others, 

 though pleasant in small qxiantity, become nauseous in larger 

 amount. The source of the odour is often a volatile oil or other 

 product contained in the glands of the plant; but in some cases 

 no such origin is found, and the source of the odour is unknown, 

 whilst its nature defies analysis. It is generally considered 



