MINUTE STRUCTURE OF PLANT HYBRIDS. 



217 



20 to 22 fi. The wood approaches more nearly in outline and disposition that of 1, while 

 the largest vasa are 15 to 16 /x across. 



The lateral bundles, which run along the leaf margin in the three, exhibit the above 

 peculiarities in an even more accentuated manner. 



Equally interesting, as in the petiole, is the occurrence along the leaf margins alike 

 in parents and hybrid of cuticular ridges, each of which is 4 fx in 1, 3 fi in 3, and 3 to 3^ /u. 

 in #. It will thus be seen that along the leaf margin in Philesia the ridges are more 

 developed than on the petiole, and approach very closely to what one finds in Lapageria. 



Sepals. — The large crimson fleshy sepals of 1 are nearly or quite the length of the 

 petals in most cases, but I have gathered blossoms on three occasions in which they were only 

 about two-thirds as long. This is of some little importance as showing that there is consider- 

 able tendency to reduction in the length of the sepals compared with the petals. At the base 

 of each, and between their lateral attachments to the receptacle, is a large, deeply-excavated 

 nectar-cavity shown in median longitudinal section in Plate III. fig. 12. On transverse 

 section it is shaped like the letter \J, except that the arms are more diverging, and from 

 the vascular bundles which run up into the sepal many branches pass inwards and are 

 richly distributed beneath the gland tissue. The gland, which is a convex pad-like 

 cushion, consists of a surface epidermal layer, the cells of which are greatly smaller and more 

 richly protoplasmic than ordinary epidermal cells, while beneath are twelve to thirteen 

 layers that are more irregular and variable in outline. I have counted several carefully 

 selected gland sections, and find that these show 170 cells in length, 50 in'width, and 13 

 deep on the average, or a total of about 1 15,000 cells. In 3 the green or reddish-green sepals 

 are at most one-third the length of the reddish-pink petals ; each is thin, slightly membran- 

 ous and inserted by a narrowed base into the receptacle. As shown in Plate III. fig. 10, 

 there is no trace of gland tissue, while the simple vascular bundles form no inferior plexus. 

 On transverse section it is convex externally. In 2 the sepals are greenish red, about one- 

 half to five-eighths the length of the petals, and rather fleshy in consistence. Each has at 

 its base a honey-gland (fig, 11), which is a raised cushion-like mass as in 1, and on trans- 

 verse section is semilunar, or nearly sickle-shaped. A rich plexus of vascular bundles 

 ramifies beneath it. The gland shows, as nearly as can be estimated, 90 to 95 cells in long 

 direction, 50 across, and 10 deep, or a total of about 45,000 to 48,000 cells. When one 

 thinks of the extreme difficulty of exact estimation here, too great stress can scarcely be 

 laid on numbers, but that the bulk of the gland is almost or exactly half that of Lapa- 

 geria one recognises when each is isolated. It may be safely inferred here, therefore, 

 since many other cases confirm it, that the reduction of the hybrid gland by half is due 

 to actual reduction in number of cells. 



On surface view the upper epidermal cells in 1 are as broad as, or broader than, long, 

 while the walls are very thin and delicate. In 3 the cells are irregularly elongate, and 

 have thickened walls penetrated by evident pore canals. In 2 the cell shape and wall 

 thickening incline rather to Lapageria, but the effects of Philesia, action are quite pro- 

 nounced. 



Lapageria 



rosea. 

 Philageria 



Veitchii. 

 Philesia buxi- 



folia. 



