62 



THE WATERLILIES. 



and less frequently in Lotos, irregular cell-masses projecting from the 

 walls ; these appear as whitish specks to the unaided eye, and are found 

 to consist of numerous oval, thin-walled, turgid cells with one end free 

 in the canal and the other attached. They develop from a single wall 

 cell, much after the manner of the diaphragms of the canals of roots. 

 Similar outgrowths were found by Mellinck (1886) filling up the air- 



*3 species and varieties examined, t 7 species and varieties examined. 



spaces of petioles of N. alba which had been wounded as far in as the 

 large air-canals. We shall speak of them hereafter as thyll-like bodies. 



The course of the vascular bundles in the petiole is longitudinal and 

 parallel from end to end. Their manner of entering the stem has already 

 been referred to. In joining the leaf, all of the bundles are connected in 

 the uppermost end of the petiole (or in the base of the leaf as one chooses 

 to call it) by transverse commissures, forming a ring of vascular tissue 

 parallel to the surface of the leaf. In Lotos this causes a circular swelling 

 of striking prominence, which I have called the "collar"; it is less 

 prominent in Apocarpiae, and not noticeable in the other groups. From 

 this ring the primary veins radiate out into the leaf. In general, the 

 bundles of the anterior and antero-lateral parts of the petiole supply the 

 lobes of the leaf, the lateral and postero-lateral its sides, and the posterior 

 and median form the midrib. 



The arrangement of the vascular bundles in the petiole differs 

 according to that of the air-canals and the size of the petiole, but follows 

 an easily definable plan. Details may be gathered from the diagrams 

 (Fig. 26). Where there are two main air-canals, we find a large double- 

 bundle at each end of the partition between the canals, that is, in the 

 median plane anteriorly and posteriorly, and two smaller bundles on each 



