1 88 
Hill and de Frame. — On the 
mini , and usually in M. linguaeforme the protoxylems of the cotyledonary 
strands are exarch before the bundles enter the hypocotyl. On the other 
hand, in M. filamentosa , M. rhomboideum , M. trigrinuni , and M. trunca- 
tellum the protoxylems referred to are not fully exarch, sometimes even 
practically endarch, although the bundles may be opened like a V. This 
feature, however, is variable ; thus in one seedling, e. g. of M . rhomboideum , 
the central seed-leaf-bundle of one cotyledon may be well divided, at a level 
immediately above the cotyledonary node, with its protoxylem mesarch or 
partly exarch in position, whilst the other bundle may show no division at 
all and the protoxylem endarch in position. 
Before passing on, attention may be drawn to a peculiarity in some 
species of this genus which is unique in the plants examined. 
In Mesembryanthemum Bolusii and M. linguaeforme , the two species 
with the fleshiest and largest cotyledons, the main central bundles of the 
seed-leaves are, for some distance above the cotyledonary node, surrounded 
by an irregular endodermis, not necessarily consisting of a single layer of 
cells, but often of two or three. In the more upper regions, the endodermis 
may not entirely enclose the bundle, but at lower levels, especially in 
M. linguaeforme, it is complete and singularly convincing. In M. fila- 
mentosa and M. rhomboideum this endodermis is not so extensive, but it 
forms a more or less complete sheath around the main bundles of the seed- 
leaves at the cotyledonary node. In these cases an endodermis surrounds 
the vascular tissues of the axis before the root-structure is organized. 
Tetragonia expansa , Murr. The transition phenomena do not differ in 
any essential feature from those of Mesembryanthemum. The main cotyle- 
donary strands bifurcate in the base of the blades of the seed-leaves, or in 
the top of the petioles, and their protoxylems become exarch before the 
bundles pass into the axis. The fusion of the laterals with the central 
strands takes place at a low level, just above the top of the cotyledonary 
tube. 
NYCTAGINACEAE. 
Abronia. The seedlings of the species of this genus examined, A. um- 
bellata and A. villosa , are of interest from the fact that the cotyledons 
are very unequal in size. Fig. 6 represents a number of seedlings of 
different ages of A. villosa\ it will be observed that in the younger plants 
one of the cotyledons is extremely small, whilst in the older plants it 
approximates more closely to the larger seed-leaf. In the youngest 
seedling (a) the rudiment of one seed-leaf is inserted on the axis at about 
the same level as the well-developed cotyledon, but in older seedlings, 
owing to the more rapid growth of the large cotyledon, the small one 
appears to be inserted lower down the hypocotyl. Also it will be ob- 
