4 6 Gibbs . — Notes on the Development and Structure of 
of the embryo-sac. with which it is so intimately fused that it can always 
be dissected out still attached to the apex of the latter. The wall of the 
pollen-tube is very thick and the contents become granular. The tubes 
are well differentiated in Heidenhain’s Iron Alum Haematoxylin. 
Seed Coat. Shows distinct specific variation. The degree of cuticu- 
larization, the form and number of cells which enlarge and the degree of 
tannin formation seem to be constant characters. Yet even in this case 
variation is more apparent than real, depending chiefly on the papillose 
manner in which the cell-wall grows out, and the nature of the secondary 
projections which occur in it. In Stellaria aquatica the cells of the 
outer integument grow out broadly, using up their whole diameter. The 
ovule in consequence appears covered with papillae as the projecting cell- 
walls are almost in contact. In Cerastium perfoliatum only the immediate 
portion of the wall in the centre of a cell is raised, and radiating projections 
round the surface of the ovule result (Fig. 24, o. i. 1). The same remarks 
hold for Spergularia satin a (Fig. 32, pap.). Stellaria media approximates 
more to Stellaria aquatica in the form of outgrowth of the individual 
cell-walls, but secondary warty projections occur in the wall of each cell 
(Fig. 22 a, sec. pap). These projections in Spergula arvensis form large 
secondary papillae, one of which may grow out from each epidermal cell 
or in some cases only from a limited number of epidermal cells (Fig. 23, 
sec. pap). In the so-called id. var. sativa, these projections are altogether 
absent, which, as the numbers are inconstant in the type, seems to hardly 
justify sub-specific distinction. 
In both Spergula arvensis and its so-called var. sativa the wall has 
a wavy cuticle which in Spergula arvensis proper is continued in the same 
form on the secondary papillae (PI. VI, Fig. 2% pap). 
Abnormalities. 
In Stellaria Holostea a case of two megaspores in one ovule was seen 
(PI. VI, Fig. 36, m). 
In Cerastium glomeratum two nucelli were observed in one ovule, each 
nucellus with a perfectly developed embryo-sac in the definite nucleus stage. 
As this abnormality has been fully described and figured in a previous 
paper ( 29 ) it is only referred to here. 
In Sagina procumbens a very interesting case of vegetative outgrowth 
of the nucellus is figured on PI. VI, Fig. 37. It occurs in a microtome 
series of the ovary and can be traced through four sections. No embryo- 
sac formation is apparent, the nucellus consisting of very actively dividing 
small cells, quite different in shape and contents from the tegumentary 
tissue of the ovule. It projects well beyond the integuments, which are not 
normally developed. In Fig. 37 the section is oblique, for while showing 
