SOLANUM TUBEROSUM 



531 



petiole are derived from further branching of the lateral groups, 

 E^ and A^, after these have become separated from the stem bundles. 

 Artschvsrager's summary of the course of the bundles follows: 



"(i) The median trace ascends 

 without fusion or forking through 

 three internodes, and then passes 

 into the petiole without branch- 

 ing. 



"(i) The lateral traces are given 

 off at the node from two of the three 

 large stem groups. 



"(3) Each large stem bundle as- 

 cends without branching in turn for 

 two internodes or for one internode. 



"(4) Where a large stem bundle 

 ascends for but one internode with- 

 out branching, it divides three times, 

 giving rise upon the first division 

 to a new stem bundle, upon the 

 second division to a new median 

 trace, and upon the third division 

 to lateral traces of the petiole. 

 Upon the division in the node, half 

 of the tissue is given off to unite 

 with that from the left (in a right 

 spiral) adjacent group, forming a 

 new large bundle directly above the 

 insertion of the leaf. Where the 

 bundle ascends for two internodes 

 without branching, it gives off vas- 

 cular tissue only for lateral traces of 

 the petiole. 



"(5) Each leaf derives its supply 

 from two large bundles and the 

 smaller one lying between these. 

 The method of derivation is uniform 

 for all leaves, the bundles taking 

 part being each time a different pair 

 from those supplying the leaf be- 

 low. In a right spiral the right 

 member of the set supplying a leaf 

 supplies also the leaf above, becom- 

 ing there the left member of the 

 set. The median trace of a given 



leaf is formed just below the third and vascular supply to leaves 

 node below the leaf it supplies." Artschwager, /o«r. Agr. Res.} 



Fig. i8i. Diagrammatic longisection 

 of stem showing course of vascular bundles 



(After 



