244 



DK J. M. MACFARLANE ON THE 



.'. Masdevallia 

 amabilis. 



g. Masdevallia 

 Chelsoni. 



.'(. Masdevallia 

 Veitchiana. 



The elements of the bundle sheath, the sieve tubes and pitted vasa, all conform in the 

 hybrid to what one might expect. 



Leaf. — Each leaf is divisible into a terminal laminar portion and basal persistent 

 petiole. Between the pseudo-bulb and petiole, also between the petiole and lamina, 

 layers of cork cells develop, which first cause shedding of the lamina, and at a much later 

 period of the petiole. 



The epidermal cells of 1 are variable in size, rounded in outline, and have thick, 

 white, refractive walls ; the cells of 3 are elongated and have thin walls ; the hybrid 

 shows a condition between the extremes. The number of stomata over the leaf area are 

 as 8 : 12 : 18, but they vary in number in any leaf over given parts of it, being sparse 

 towards the base and apex, abundant over the middle two-thirds. A careful comparison, 

 therefore, of the whole area requires to be made to obtain this result. 



The mesophyll tissue that surrounds the bundles alike of petiole and lamina in 1 consists 

 parti}' of quadrangular cells, whose thickened walls show slit-like deficiencies with pore 

 apertures. One can readily trace that the slits follow an oblique, almost spiral course 

 round the wall, but the thickened areas between are too broad to give even the semblance 

 of a spiral marking to it (Plate VII. fig. 1). In 3 the mesophyll throughout, but specially 

 that towards the base of the lamina, is crowded with oval or quadrangular cells, larger 

 by half than the slit cells of the last, while the walls exhibit beautiful spiral thickening 

 (Plate VII. fig. 2). The secondary spiral thickening bands are of considerable thickness, 

 as one can learn from sections. The hybrid shows fewer spiral cells ; in truth, towards 

 the leaf apex they become very rare, and the spiral deposit is less in amount, but these 

 peculiarities demonstrate the moulding action of the other parent. From careful com- 

 parison of the parent and hybrid cells, I incline to view the spiral cell as a modification 

 of the slit-marked or pitted one through great elongation in oblique or spiral direction 

 of the slits. Examples can be got in the hybrid where greatly elongated and oblique 

 slits alternate with thickened bands. 



Apart from the question of hybrid production, it is worthy of note that the 

 parents could be easily distinguished from each other histologically by the presence or 

 absence of spiral cells in the leaf tissue, though the leaves are strikingly alike to the 

 naked eye. 



Perianth Segments. — The three sepals which form the most attractive part of the 

 flower are of a uniform purple-red tint in 1 ; in 3 the inferior halves of the two lower 

 sepals are of a yellow-red colour, flushed with purple, while the upper halves and superior 

 sepal are either bright red or may have a faint purple flush ; the hybrid has a pretty 

 wide distribution of the purple flush over the inferior sepals and the ground colour is 

 more subdued than in the last, but richer than in the first. This colour distribution is 

 proved on microscopic examination to be due to bladder-like hairs filled with a purple 

 cell-sap. These spring from the epidermal tissue, the cells of which contain yellow 

 chromoplasts. In 1 the epidermal cells are irregularly rounded in outline, and they, 

 as well as subjacent cells, have a small number of minute pale yellow chromoplasts, 



