MINUTE STRUCTURE OF PLANT HYBRIDS. 



235 



two sizes ; one set of seven to eight are early differentiated, remain distinct from l. 

 the sheath, and are oval in shape. Another set of smaller size, and numbering eight 2. 

 to twelve, are intercalated between these, and are nearly wedge-shaped. The first set s. 

 show small external stereome patches, whose elements are little thickened, and the 

 largest element is 14 /x across. The phloem is a dense patch of sieve tubes and cells 

 differing little in size, the largest tube measuring 10 jx across; the xylem is a narrow 

 band of spiral tracheids and xylem cells, the largest averaging 15 fx. The intercalated 

 bundles consist only of a small patch of phloem and xylem lying against the sheath. In 

 2 the bundles number fourteen to sixteen, and exhibit less disparity than do those of 3. 

 They are all more or less united with the sheath, though, as in the latter parent, the 

 larger ones tend almost to separate, and in such cases a distinct stereome patch is 

 developed, the largest elements of which measure 16 to 17 /x across. Curiously enough, 

 while the phloem in appearance and size of its constituent elements rather approaches 

 to that of 1, the xylem equally leans to that of 3. 



Sepals. — In S. Geum, as in other members of its' section, the sepals are inferior, and 

 after expansion of the flower curve backwards, and become adpressed to the flowering stem 

 (Plate VI. fig. 8). The apex is rounded, and carries a single water stoma with associated 

 epithem tissue that terminates the bundle. In S. Aizoon the sepals are superior, 

 and in expansion grow outwards and upwards, so as to make an angle of 25° to 30°, 

 with the ideal prolongation upwards of the axis (Plate VI. fig. 10). The apex is acute, 

 often terminated by a knobbed hair, and usually three water stomata, one terminal and 

 two lateral, are at the ends of the vascular bundle. In S. Andrewsii the sepals are 

 recurved, so that they make an angle of 125° to 130° with the ideal axis (Plate VI. 

 fig. 9). The apex is obtuse, and there is one water stoma ; very rarely two or three. 

 One could scarcely choose a better series of naked-eye objects on which to demonstrate 

 the comparative position assumed by parent and hybrid parts than those now referred to. 



On flower-stalk, bracts, and sepals alike there are glandular hairs, which in 1 have a 

 delicate stalk of four to five cell rows and a small rounded glandular head ; in 3 the stalks 

 are stout, usually short, and consist of seven to eight cell rows, while the heads are fully 

 a half larger than those of 1. Both types of hair are reproduced in the hybrid, 

 though less abundantly. The upper epidermal cells in 1 are straight- walled, in 3 they 

 are wavy, and in the hybrid sinuous. 



Petals. — In 1, which is the least specialised form, the epidermal cells of the upper 

 surface are prolonged into slight papillae, in 3 they grow out as hair processes, and in % 

 they are intermediate in length. A peculiarity in colour distribution is that the petals 

 of 1 are marked with little crimson and yellow spots towards their base, those of 3 have 

 only large deep crimson spots, while in the hybrid the crimson spots alone appear, no 

 flowers hitherto examined having shown traces of yellow. 



Stamens.— The anthers of 1 are of a pale pink colour, those of 3 are of a greenish- 

 yellow colour, and both contain abundance of good pollen. The anthers of 2 are of a 

 pale pink-green or pink-yellow colour, but the pollen is bad, the grains being variable in 



VOL. XXXVII. PART I. (NO, 14). 2 M 



Saxifraga 



Geum. 

 Saxifraga 



Andrewsii. 

 Saxifraga 



Aizoon. 



