56 TENOPYR: CONSTANCY OF CELL SHAPE 
2. A small-celled group, the first leaf from the summit having 
stomata whose average length is 0.054 mm., those of the third leaf 
being 0.067 mm. long. 
In his paper on species hybrids of Digitalis, Neilson Jones 
(1912) does not give any measurements of the cell size of D. grandi- 
flora and D. purpurea; but his general observations are most in- 
teresting. He finds that D. grandiflora, which has smaller leaves 
than D. purpurea, has larger leaf cells. Hybrids of these two 
species are intermediate in both external and cytological charac- 
ters, but in both respects there is a tendency to favor the seed 
parent. Thus, in the hybrid resulting from the cross | hee ae Gas 
¢ the leaves are somewhat larger and the cells smaller, than they 
are in the progeny of the reciprocal cross. Evidently the size of 
the leaves and cells of the hybrids cannot be due to heterozygosity, 
since in that case we would expect the reciprocal crosses to have 
the same effect on the leaf and cell size of the resulting hybrids. 
One of the most careful studies of the relation between body 
size and cell size is that of Sierp (1913). _He made measurements 
of the cells of various tissues of dwarf and normal plants, the 
dwarfness being in some cases a fluctuating characteristic, in other 
cases hereditary. Under the first group come dwarfs of Panicum 
sanguineum, Draba verna, Aethusa Cynapium and Urtica dioica. 
This type of dwarfs always had cells more or less reduced in size. 
Some of the differences in cell size were very slight. True, that is, 
hereditary dwarfs, he found were of three kinds: 
1. Those having smaller cells than the normal plants, as certain 
dwarf varieties of Solanum tuberosum, Pisum sativum, Clarkia 
pulchella, and Zea Mays. 
2. Dwarfs with cells slightly smaller than, or almost the same 
as, those of the normal type, as those of Lathyrus odoratus, Mira- 
bilis Jalapa, Phaseolus vulgaris, and Lens esculenta (Rote Kleine 
Winter). 
3- Dwarfs with larger cells than found in the normal plants, 
as Nigella damascena nana. 
Sierp found great variability in the cell size of each tissue, 
though the average value was quite constant. He lays great 
stress on the importance of measuring exactly corresponding 
_ places, when comparing cell size of any tissue of the stem or leaf, 
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