2i8 J. H. Priestley and R. M. Tupper-Carey 
Rubus Idceus L. and Camellia Japonica L., it is possible to state 
quite definitely that when the stem growing point is developing 
freely in light, no primary stage of the endodermis with typical 
Casparian strip precedes the formation of the secondary endodermis. 
The stem apex is also in possession of a cuticle from its earliest 
growth in the seedling. Its presence makes it more difficult to 
investigate experimentally the permeability of the meristem. Stems 
of Vida Faba L. and Phaseolus vulgaris L. were used in these experi¬ 
ments, short lengths bearing apical buds, with all lower nodes cut 
away to avoid leakage before the pressure reaches the apex. These 
stem apices were mounted in pressure tubing in the same type of 
apparatus as in the previous experiments (p. 212) and water, some¬ 
times with various dyes in solution forced into the stem. 
The water thus forced into the vessels at the cut end will be 
unable to make its way out, even if the apical meristem is per¬ 
meable, so long as the cuticle is unbroken, but directly a small tear 
is made in the cuticle the liquid oozes out from the surface, if the 
liquid is under pressure of half an atmosphere or more. The simplest 
way of demonstrating this fact is to pierce the cuticle with a very 
fine glass capillary, the liquid then soon rises in the capillary tube. 
Occasionally it will be found necessary to withdraw the capillary 
slightly after its first entry as it may get blocked with crushed 
tissue. These experiments suggested that the meristem at the stem 
apex was much more permeable to water. 
Experiments with dyes in solution in the water forced in, 
brought to light further differences between stem and root. If acid 
dyes are used, in which the molecular grouping responsible for the 
colour behaves as an electro-negative ion, the dye penetrates 
rapidly the cells at the growing apex and the liquid oozing immedi¬ 
ately from any scratch in the cuticle will be coloured with the dye. 
Even when the cuticle is left intact, the dye finds its way into the 
apical cells in a few hours. On the contrary, basic dyes, in which 
the colour group is electro-positive, do not penetrate the apical 
protoplasts and the liquid oozing from a cut, or driven up an inserted 
capillary tube, is colourless. In this case the dye is probably held 
back by the walls of the cells, either by adsorption or chemical 
reaction: the evidence in favour of the two alternatives will be 
found in the papers of Wieler( 29 ) and Sven-Oden( 27 ). Not only, then, 
is the stem apex relatively permeable, but it stains readily with 
acid dyes, whilst the root apex is relatively impermeable and only 
stains with basic dyes. 
