288 GLANDULAR HAIRS. [Chap. XV. 



beneficial. Nor can the benefit be quite so insi(?nificant as 

 it mifirlit at first be thought, for a moderately tine plant of 

 Primula sinensis bears the astonishiufi: number of above two 

 millions and a half of glandular hairs," all of which are able 

 to absorb ammonia brought to them by the rain. It is more- 

 over probable that the glands of some of the above-named 

 plants obtain animal matter from the insects which are oc- 

 casionally entangled by the viscid secretion. 



CONCLUDING REMARKS ON THE DROSERACE.E. 



The six known genera composing this family have now 

 been described in relation to our present subject, as far as 

 my means have permitted. They all capture insects. This 

 is affected by Drosophyllum, Roridula, and Byblis, solely by 

 the viscid fluid secreted from their glands; by Drosera, 

 through the same means, together with the movements of 

 the tentacles; by Diona?a and Aldrovanda, through the 

 closing of the blades of the leaf. In these two last genera 

 rapid movement makes up for the loss of viscid secretion. 

 In every case it is some part of the leaf which moves. In 

 Aldrovanda it appears to be the basal parts alone which con- 

 tract and carry with them the broad, thin margins of the 

 lobes. In Dionaa the whole lobe, with the exception of the 

 marginal prolongations or spikes, curves inwards, though 

 the chief seat of movement is near the midrib. In Drosera 

 the chief seat is in the lower part of the tentacles, which, 

 homologically, may be considered as prolongations of the 

 leaf; but the whole blade often curls inwards, converting the 

 leaf into a temporary stomach. 



My son Frnncls connted the eluded) wns found by a plnnim- 

 baira on a spaee measured by eter to be .3!i.28r Honnre inclieH: 

 means of a mierouieter, and so that the area of both surfaees 

 found that there were :C),336 on was 78.57 K(iuare Inches. Thus 

 a square Inch of the upper sur- the phmt (excluding the flower- 

 face of the leaf, and 30,035 on stems) must have lioriie the as- 

 the lower surface; that Is. in tonlslilujj number of 2.5U8,()9U 

 about the prrjportlon of 100 on Kliindular hairs. The hairs were 

 the upper to 8.) on the lower sur- counted late In the autumn, and 

 face. On a sipiare Inch of both by the following spring (May) the 

 surfaces there were (!5,;i71 hairs. leaves of some other plants of 

 A moderately fine plant bearing the same lot were found to be 

 twelve leaves (the larger ones be- from one-tliird to one-fourth 

 Ing a little more than two Inches broader and longer than they 

 in diameter) was now selected, were before: so that no doubt 

 and the area of all the leaves, the Klandular hairs had Increased 

 together with their footstalks In number, and probably now 

 (the flower-stems not being in- much exceeded tliree millions. 



