99 
Endodermis in the Stem of Hippuris . 
connected with a description of one particular specimen. There is a wide 
variation in dimensions of the stem at the apex which is associated with dif- 
ferences in the number of periblem caps and bulk of the plerome. The 
number of the former may even vary in one and the same apex, as, for 
instance, in one specimen examined there were five caps on the one side of 
the stem and four on the other. The results of this investigation therefore 
confirm the observations of Schoute, and emphasize his conclusion that the 
endodermis cannot be regarded as a layer of definite morphological value. 
That is to say, its ontogenetic history is shown to be variable as elucidated 
by a study of cell-lineage. The only criterion of morphological identity in 
such instances would have to reside in the structure of the completely 
differentiated tissues, irrespective of their cellular history. This was, speak- 
ing generally, the position adopted by Van Tieghem, and whilst it illustrates 
the plasticity of the plant cells in differentiating into this or that form 
of tissue, it emphasizes the abstract character of the so-called morphology 
of the tissues themselves. 
References. 
1 . Schoute, J. C. : Die Stelar-Theorie. P. Noordhoff, Groningen, 1902. 
2 . Sanio, C. : Ueber endogene Gefassbiindelbildung. Bot. Zeit., xxii Jahrgang, 1864. 
