MINUTE STRUCTURE OF PLANT HYBRIDS. 237 



I cannot as yet say whether they merely excrete a cool, watery juice, or, in addition, some ]■ Er i ca Tetraiix. 

 sweet excretion. The morphology of these nectaries, in any case, is highly instructive. *■ Erica ciliaris. 



(f) Erica Watsoni, x . 



This hybrid between E. Tetraiix and E. ciliaris was first found in a wild state by 

 Mr H. Watson* at Truro, Cornwall, where both parents occur. Considerable quantities 

 of it have been gathered, and from these supplies have been obtained for the Edinburgh 

 Botanic Garden. 



Stem. — The structure in the three is very similar throughout, except that the pitted 

 vasa in the xylem of 1 are few in number, and 12 to 15 /x across in the largest 

 examples ; those of 3 are pretty abundant, and 20 to 22 m across ; in 2 the number 

 is intermediate, and the diameter varies from 16 to 20 ,«, the majority inclining 

 towards 3. 



Leaf. — On surface view, the upper epidermis shows straight walled, pentagonal, 

 or hexagonal cells, which are 30 /* across. Many of these develop long, delicately- 

 striated hairs from the upper end of the cell. In 3 the cells are slightly elongated, 

 with wavy walls, are 50 to 60 m across, and only towards the leaf apex are a few striated 

 hairs encountered. In 2 the cells are sinuous-angular, and nearly isodiametric, 40 

 to 45 m across, and hairs are irregularly and sparingly scattered over the lower leaf 

 portion, becoming more abundant towards the apex. 



Transverse leaf-sections of 1 give a thickness of 200 to 250 /x ; of 2, 270 to 330 m ; of 

 3, 350 to 400 ju,. The revolute leaf margins of 1 leave about one-third of the leaf 

 epidermis exposed ; the margins of 3 are slightly turned back, but at least five-sixths of 

 the lower epidermis is exposed ; in 2 a full half is exposed. The proportion of palisade 

 to loose parenchyma in the three is as 1 : If : If. The vascular bundle of the leaf 

 in 1 is strengthened below by a sclerenchyma mass of eighteen to twenty-two elements, 

 and above of ten to fourteen ; in 3 the lower mass is absent, but the upper is developed, 

 and consists of fourteen to eighteen elements ; in 2 there is a lower mass of from 

 nine to thirteen elements, and an upper of from twelve to sixteen. 



Petals. — The corolla of 1 is regular and ovate-urceolate ; that of 2 is very slightly 

 irregular, ovate-constricted, and slightly gibbous towards the base ; that of 3 very 

 irregular, oval below, contracted above, and with pronounced enlargement of the upper 

 part of the corolla. The average colour of 1 is a waxen whitish pink, of 2 crimsoD-pink, 

 of 3 a dull purple-crimson. The outer epidermal cells of 1 all grow out into pronounced 

 surface papillae, in 2 the papillse merge gradually into the basal part of the cells, in 3 the 

 free cell-surfaces are only slightly elevated. 



Stamens. — The anthers of 1 develop tails that are 9 to 10 mm. long, and the cells of the 

 outer anther wall are papillose, like those of the petals ; the anthers of 3 are devoid of tails, 



* Hooker and Arnott's British Flora, 6th edit. 



