234 



DR J. M. MACFARLANE ON THE 



/. Saxifraga 



Geum. 

 8, Saxifraga 



Andrewsii. 

 ;. Saxifraga 



Aizoon. 



form enclosing masses round the island-like stomatic clusters. Further, there are small 

 cells with dense contents which connect the stomata in each island. In 3 all the cells 

 are nearly uniform, and are straight or faintly sinuous in their walls ; the stomata also are 

 pretty uniformly distributed, so that they cannot be said to fall into island masses. In 

 2 the isolation is evident, as is also the separation into two kinds of cell, though in shape 

 and size they are quite intermediate. The cells along the midrib region are note- 

 worthy, for one can readily trace in these how evenly the hybrid is between the parents. 

 Equally instructive are the under cells of the serrations. 



On transverse section the leaf of 1 exhibits a thin cuticle above and rather thicker 

 one below ; that of 3 has a thick upper and thin lower cuticle ; and in 2 they are equal in 

 thickness. In 1 there is one deep columnar and a second shallower and more irregular 

 palisade layer, passing into loose parenchyma. In 3 there are four to five closely-packed 

 palisade layers, of which the uppermost is deeply columnar ; the lower are more rounded, 

 and pass sharply into the loose parenchyma. In # there are three to four layers, of which 

 the uppermost is columnar and the others rounded-elongate. The chloroplasts in 1 are 

 large, numerous, and give a dense red aspect to the cells when stained by eosin ; in 3 they 

 are small and scattered, so that when stained the cells appear pale, with red spots. In 2 

 some of the cells incline to the one condition, and some to the other. The spongy 

 mesophyll of 1 consists of about seven layers, whose cells are large, loose, and stellate or 

 branching in character ; in 3 they are densely packed and rounded, so that the inter- 

 cellular spaces are small, while they average one-half to three-fourths the size of the former. 

 The size, mode of packing, and contents of the hybrid cells are quite intermediate. 



Flowering Stem. — In large mature stems of 1, near the radical rosette of leaves, the 

 cortex cells are seven to eight layers deep, and pass abruptly into a well-formed scleren- 

 chyma sheath of six to eight layers. The largest elements of this sheath are 25 fx across, 

 and the walls are so thickened in most as to reduce the lumen to one-third its original 

 size. The internal matrix tissue consists of large and tolerably uniform cells. In 3 the 

 cortex consists of twelve to thirteen cell layers, which also pass abruptly into a scleren- 

 chyma sheath though of narrower proportion than in the last, since the elements are 

 smaller, though the layers are as numerous. The largest elements are 20 to 22 ll across. 

 The amount of secondary thickening in these is much less, the lumen bearing a ratio to 

 the original cavity of seven-eighths. The internal matrix tissue is made up of small 

 cells externally, and of larger central ones, none of which, however, equal those of i. 

 The hybrid in all of these points is intermediate, the thickening of the sclerenchyma cells 

 being specially noteworthy. 



The bundle system in 1 consists of eight to ten wedge-shaped strands, whose bases 

 are set against the sclerenchyma sheath. The phloem part has a mass of stereome fused 

 with, and scarcely distinguishable from, the sheath, the largest stereid being 20 /x across. 

 Internal to this is the phloem proper, made up of large sieve tubes — the largest measuring 

 about 30 fx across — and companion cells. The xylem tracheids are very uniform in size, 

 aggregated as a wedge-like cluster, and are 18 to 20 ju, across. In 3 the bundles are of 



