184 
Surrounding the nucellus is the integument. Before fertiliza- 
tion it presents the usual form as seen in the oyules of other 
plants, but after fertilization it develops rapidly, assuming an in- 
flated sac-like form, and in the majority of species greatly ex- 
ceeds the nucellus in its growth. The seeds are anatropous and 
sessile ; and when removed from the placenta the location of the 
hilum is marked by an opening. This is caused by the shrinking 
or, possibly, by the partial absorption of the chalaza, remains of 
which may still be seen in the ripened seed. This leaves the in- 
tegument alone connected with the placenta. The free ends, 
therefore, lend to the seeds the appearance of an arillus, the open- 
ing at what seems to be the apex being due to the bending in of 
the cells of the inflated integument as they approach the hilum. 
The testa is the conspicuous feature of the seed, and with the 
embryo furnishes one of the family features or distinguish- 
ing characters of the order. It is composed of cells of varying 
forms, as seen in the plates. The outer margins of the cell wall 
are much thickened. Thus the testa presents in its outward as- 
pect a ribbed surface, and gives to the seed a cage-like appearance. 
In Pogonta ophioglossoides the so-called ribs (thickenings) do not 
correspond to the cell divisions, but form long bands over the 
length of the testa, branching and running together somewhat at 
either extremity, (fig. 19, Plate CLII.). The sides of the cells, 
as well as all the other margins, are extremely delicate and color- 
less. The inner face of the cell often receives an elegant sculp- 
turing from delicate bands that are quite characteristic of the 
several species in which they occur. These lines are noticeably 
stronger towards the base of the testa in some species, quite 
fading out atthe apex. This faulty development of the nucellus to- 
gether with the delicacy of the seed coat is doubtless the cause of 
the relative scarcity of Orchids. Remembering the large number 
of pods usually produced by each plant and that each pod: con- 
tains something like six thousand seeds, we realize the enormous 
fatality among the seeds. This is not in any way connected with 
a lack of fertilization. The classical work of Darwin has demon- 
strated the completeness of this process, were it necessary to go 
back to the flower to ascertain the fact. The whole appearance 
of the seed is that of a waif, poorly developed and insufficiently 
