202 IMF. PLANT WORLD 



ci'titral of Mexico, and extending their range into southwest- 

 ern lexas Both plants have of recent years been brought' 

 into economic prominence by virtue of the fact that they se- 

 crete rubber, guayule being the more important plant in this 

 regard, since the amount of the substance sought for in com- 

 m;;'*ce is much too small in iiiariola to make it worth while to 

 exploit it. I he two illustrations which are presented will 

 serve at oncc i.o contrast these interesting plants. It may be 

 added by wa\ of orientation that they are members of the 

 Compositip, bi't are peculiar in having only tixe ray-Howers in 

 the head, these only being capable of producing seed. The 

 disc flowers ae all staminate, but the style grows after the 

 usual fashion In the Compositae, serving to eject the pollen. 

 Reproduction takes place readily and very generally by means 

 of seed, though the contrary has been intimated,* but these 

 two species ha\e markeci methods of vegetatixe reproduction 

 which complf.nent the method by seed, and are further of 

 interest in thai they are not common to the two species. It 

 would be cjuile useless to speculate how this condition has 

 come about, so that we shall turn directly to the facts. Ihey 

 are especially worth recording not only because they have 

 ne\er been studied with care and indeed ha\e been entirely 

 o\erlooked by those w'ho ha\'e essayed to study the plants 

 hitherto, but because of a cin^idus bearing on the problem of 

 grafting bet\\een the two species in question, a suggestion 

 which has been made, but to my knowledge never carried out. 

 lurning first to guayule Vv'e note that this plant regularly 

 produces new indi\-iduals by sending up new shoots {"reton- 

 yo.v") from the roots, recalling the behavior in orchard trees, 

 but more definitely adjusted to reprociuction than is usual I 

 believe. The root system of the guayule consists of a tap 

 root, a great many short laterals running in all directions, 

 and upward of a dozen \ery long secondary roots placed at 

 a slight depth in the soil, and of small calibre, ^ nmi. or often 



*Ross. H., Dei' Anuloniischt,- Ba.u lU-r .Mexikani.schen Kaiil.srluiki>ll;u)ze 

 "Ouaviil.." P,cr. d. Bi)t. GfSfllscli., 26a: lMS-263 . Ap. 1908. 



