3^4 



THE POPULAR SCIENCE MONTHLY, 



Again, a species of the allied genus Lathy rus (Fig. 19), L. amplii- 

 carpos^ affords us another case of the same phenomenon. 



Other species possessing the same faculty of burying their seeds 

 are Okenla hypogcea^ several species of Conimelyna, and of Amp)hi- 

 earpcea^ Yoandzeia subterranea, Scrophularia arguta, etc. ; and it is 

 very remarkable that these species are by no means nearly related, but 

 belong to distinct families, namely, the Cruciferce, Leguminosca, Coni- 

 inehjnaceci?^ ViolacecB, and Scrophulariacem. 



Moreover, it is interesting that in L. amp)liiGarpos^ as in Vicia 

 amphicarpa and Cardamine chenopodifoUum, the subterranean pods 

 differ from the usual and aerial form in being shorter and containing 

 fewer seeds. The reason of this is, I think, obvious. In the ordinary 

 pods the number of seeds of course increases the chance that some will 

 find a suitable place. On the other hand, the subterranean ones are 

 carefully sown, as it were, by the plant itself. Several seeds together 

 would only jostle one another, and it is therefore better that one or 

 two only should be produced. 



In the Erodiums, or cranesbills, the fruit is a capsule which open 

 elastically, in some species throwing the seeds to some 

 ^ little distance. The seeds themselves are more or less 



spindle-shaped, hairy, and produced into a twisted hairy 

 awn as shown in Fig. 20, representing a seed of JE. glau- 

 cophyllum. The number of spiral turns in the awn de- 

 pends upon the amount of moisture ; and the seed may 

 thus be made into a very delicate hygrometer, for, if it 

 be fixed in an upright position, the awn twists or un- 

 twists according to the degree of moisture, and its 

 extremity thus may be so arranged as to move uj) and 

 down like a needle on a register. It is also affected by 

 heat. Now, if the awn were fixed instead of the seed, 

 it is obvious that, during the process of untwisting, the 

 seed itself would be pressed downward, and, as JM. Roux 

 has shown, this mechanism thus serves actually to bury 

 the seed. His observations were made on an allied 

 species, Ei^odium cicoiiiimi, which he chose on account 

 of its size. He found that, if a seed of this plant is laid 

 on the ground, it remains quiet as long as it is dry; but 

 as soon as it is moistened i. e., as soon as the earth be- 

 FiG. 20. Erodtum comes in a condition to permit growth the outer side 



GLAUCOPIITI-LUM. , T i ^ T i 



(After Sweet.) 01 the awn contracts, and the hairs surroundnig the 

 seed commence to move outward, the result of which 

 is gradually to raise the seed into an upright position with its point 

 on the soil. The awn then commences to unroll, and consequently to 

 elongate itself upward, and it is obvious that, as it is covered with 

 reversed hairs, it will probably press against some blade of grass or 

 other obstacle, which will prevent its moving up, and will therefore 



