The Origin of the Endodermis in the Stem of Hippuris. 
BY 
KATE BARRATT, B.Sc., 
Demonstrator in Botany , Imperial College of Science and Technology , London. 
With six Figures in the Text. 
T HE question of the three germinal layers exhibited by the stem 
and root of Dicotyledons is a very old one, and has been the subject of 
investigation by many botanists. The idea that these three developing layers 
were the initials of definite tracts of tissue of the adult plant was first put 
forward by Hanstein. He supposed that of these three layers or histogens, 
the dermatogen gave rise to the epidermis, the periblem to the cortex, and 
the plerome to the central cylinder. 
The fact that in the adult organs the innermost layer of the parenchyma- 
tous tissue surrounding the central cylinder is frequently differentiated 
by special characters has given to this layer, the endodermis, a special 
significance. The reason that it has acquired so much importance is that 
it has generally been regarded as the innermost layer of the cortex and 
developed from the innermost layer of the periblem, forming thus the 
boundary of the stele. 
The importance of the endodermis as a morphological unit thus 
obviously depends on the uniformity of its mode of origin. This was 
realized by Schoute (1), who in 1902 published a general review of the stelar 
theory, and incidentally made a critical examination of a number of stems 
and roots. He showed that the majority of species examined exhibited 
a well-marked endodermis. The origin of this layer from the apical tissue 
of the stem was investigated in the case of only six species, in some 
of which no distinction between periblem and plerome could be made 
out. Among the plants examined was Hippuris vulgaris , in the stem of 
which the apical structure is so clear that it has become a classical type 
for use in the laboratory. 
Schoute, using series of transverse and longitudinal sections, traced the 
history of the development of the tissues from the apex to the mature part 
of the plant, and was led to the conclusion that here not only the endodermis, 
but several other layers of the cortex were derived from the plerome. 
[Annals of Botany, Vol. XXX. No. CXVII. January, 1916.] 
