COURSE OF THE BUNDLES IN THE STEM. 



271 



the other rather smaller one {2m) is the median bundle of the next higher leaf. At 

 each end of the longer diameter is a small bundle (2, 2): these are the lateral 

 bundles of the last-named leaf. On both sides of each lateral bundle, that is opposite 

 each corner of the rectangular transverse section, there is further a small cauline 

 bundle {s, s). The median bundles appear first, then the lateral ones, and the 

 cauline bundles much later. At an early stage irregular anastomoses appear in the 

 nodes between all of them, the small cortical bundles of sieve-tubes and fibres also 

 taking part in these (p. 232). 



Among the other Potamogetons which have been investigated, P. perfoliatus 

 has fundamentally the same bundle-system. Also the rhizome of P. pectinatus 



Fig. 121. — Potamogeton natans (40). End of the stem, made transparent ; the outer I.iyers of tissue removed in 

 the lower part by longitudinal sections; successive leaves and their belongings numbered in order, fn median 

 bundle ; / lateral bundles of the leaf indicated by the figures ; t the united portions ; a a bundle of leaf 4 which runs 

 an exceptional distance separately. The median planes of the leaves i — 3 lie alternately right and left in the plane of 

 the paper (opposite the middle of ? is the axillarj' bud belonging to it). Above 3 is a rotation, so that the median 

 plane of leaf 4 is at the front, while that of 3 is at the back. The median bundle of 5, 57«. therefore runs deep down 

 into the preparation. The lateral bundles of i and the cauline bundles are (as yet) not visible ; o = the stipular sheath 

 of the base of the leaf. 



appears, according to an incomplete investigation, to resemble it. In other species 

 the structure resembles that described, but is simpler, and reduced in proportion to 

 the average decrease in size of the leaves. 



P. lucens and P. gramineus have a leaf-trace consisting of a single bundle, which 

 does not divide into three bundles till its exit at the node into the leaf. Each passes 



