40 



MICHIGAN ACADEMY OF SCIENCE. 



PAPERS READ IX THE SECTION OF P.OTANY. 



THE RELATION OF THE FjIBRO-VASCULAR BUNDLES 

 THE ROOT AND HYPOCOTYL IN ECHINOCYSTIS 

 LOBATA TORR. & GRAY. 



IN 



JAS. B. POLLOCK, SC. D. 



In the commou wild cucumber. Ecliiuocvstis lobala. Tori-. ^: (ria\', llie 

 writer has observed some facts conceruiug the transition of the tibro- 

 vascular bundes from the root to the h^pocotyl, that seem not to have 

 been described or observed by previous writers on the subject of Tliis 

 transition. The new facts concern the change in number of bundles, 

 which is four in the root and six in the upper part of the hyi)ocotyl. 

 as Lamounette^ found in Cucurbita maxima and Cucumis melo. The seed- 

 ling of Echinocystis ditfei's in several particulars from those of most 

 of the other Cucurbitacea^ examined by the writer. First it does not 

 develop a special organ for holding the seed coats in germination as 

 most of the Cucurbitaceae do. Second, two whorls of vigorous se<- 

 ondary roots, with four roots in each whorl, are developed very early 

 in germination. These whorls are usually 2-4 muL apart, and situ- 

 ated at the top of the primary root, the upper whorl marking the 

 point where ai)parently the root leaves oft" and the hypocotyl begins. 



A stiidA' of cross sections shows that only below tln^ second whorl 

 of secondary roots does th<' ])rimary root show llie typical loot struc- 

 ture, with four sets of xyle.m bundles alternating with f(»ur sets of 

 l)hloem bundles. The secondary roots of the lower whorl are opposite 

 the xylem bundles of the primary root, lietween the two whorls of 

 secondaiy loots Ihe rearrangement of the xylem bundles takes place 

 just as described by Lamouuette in Cucurbita maxima. Each xylem 

 bundle of the juimary i-oot sejtarates into two ]»arts. each of which, 

 for some distance takes a secant ])osition, then unites with a similar 

 l)art from a nt^ghboiing xylem bundle, the two finally f(U'ming a single 

 xylem bundle lying internal to the c()rres])onding ])hloem bundle. In 

 Echinocystis this change is comj)leted at the 1(m<"1 of the u]»per whorl 

 of s(M-ondarv loots. so that at this ])oint therc^ are four collateral 

 l)undles, with the secondary roots lying op])osite the sjiaces between 

 them and directly over the roots of the lower whorl. So far then as 

 the relative ]»osition of xyhun an.d ]»hloeui are coucerued, the change 

 from root bundles to stem bundles is completed at the level of tlie 

 upper secondary roots, and here the number of bundles is the same 



'Lainounette, — Recherches sur I'origine morphologique du 

 Ann. d. sci. nat. Ser. 7, 11: iy;i-L'T(<, 1890. 



liljer interne. 



