MORPHOLOGY AND ANATOMY OF THE NYMPH.EACE.^. 297 



In aH cases where tubers are produced in the Nymph(cacc(B the first or first two 

 internodes of tlie new growth resulting from their gerininatioii develop into thin stolons, 

 in Nymphwaflava about 5 cm. long, which swell out at their extremities to form new 

 rhizomes (PI. XXII. fig. 18). And it is a very remarkable fact that the first leaves 

 borne on these rhizomes are submerged ones, entirely similar to the embryonic leaves 

 of the young seedling, except that the very first leaf of all is not truly acicular, but 

 possesses a very small lamina. 



When these new growths arise from buds upon a primary runner or stolon, as in 

 N, jlava, they may be called secondary stolons. They contain 4-7 vascular bundles (in 

 fig. 19, 4 only), and the exact manner in which they are arranged varies from one stolon 

 to another, and even in the different regions of the same stolon ; thus, a varying number 

 of them may be united in pairs, or they may be all separate and distinct. In fig. 19 

 there are tw^o separate bundles, and two fused to form a pair. Sometimes six bundles 

 are present, and these are fused together so as to form two pairs ; then the resemblance 

 that such a section bears to one of the floral peduncles of Cabomba aquatica is most 

 remarkable, for here also tbere are six bundles almost identical in appearance, and also 

 united into three pairs. The vascular bundles of the secondary stolon are exactly 

 similar to those described in the primary. Tlie phloem groups are very prominent, with 

 an outer cap of phloem parenchyma, within this a mass of large sieve-tubes witli 

 their companion cells, and then a few small xylem elements at their inmost points, the 

 jxisition of the earlier-formed elements being as before occupied by a canal formed by 

 their disintegration ; and finally each bundle or pair of bundles is surrounded by a very 

 clear endodermis. As the runner approaches its termination, where it becomes con- 

 verted into the new rhizome, it increases very much in girth, the internodes between the 

 first leaves, which are borne at this point, being very short and thick. The vascular 

 bundles, whether single or in pairs, increase in size, lose their regularity, and fuse 

 laterally with each other. At the same time they subdivide so as to form so many 

 groups of bundles which partially recover their identity after each node, although less 

 and less distinctly as you pass higher up in the stem, until at last the usual structure of 

 the rhizome is attained. 



It is especially to be observed in some species that those rhizomes which take their 

 origin in this manner from such secondary stolons have their vascular bundles, 

 throughout the whole rhizome, more or less gathered into groups around different 

 centres, o-enerally three, forming groups which correspond to those found at the base. 

 All the bundles in each group direct their xylems towards the point around which they 

 are arranged ; and so it comes to pass that in these rhizomes the inner bundles of the 

 vascular mass are, for the most part, inversely oriented, which point has been previously 



referred to. 



A similar grouping is seen in the tubers of A. h'heroso, which are borne on the 



polystelic stalks mentioned above. 



