i86 



SIZE A FACTOR IN STELAR MORPHOLOGY 



[CH. 



the secondary will form an efficient gas-barrier, cutting off the outer ventilating system of 

 the cortex from the vascular tissues within its circle. 



Seen in surface view the Caspary-band appears relatively broadband it is found to be 

 pitted (Fig. 177, i), but no protoplasmic continuity appears to be established either between 

 the endodermal cells and cells of the cortex, or on the other hand with cells of the vascular 

 strand. The endodermis is thus a structurally isolated tissue, which places the control of 

 transit inwards and outwards upon the efficiency of the protoplasts of its cells. The less 

 highly specialised type of endodermis which is called primary is found to be characteristic 

 of the Ophioglossaceae, the Osmundaceae, and the Marattiaceae, and it is found also in 

 the Hymenophyllaceae. These are all famihes of Ferns which on grounds of general 

 comparison may be held as relatively primitive. 



The secondary type of endodermis is found in all the other Filicales, and in general in 

 the Phanerogams. It is characterised by the deposit of a layer of suberin on the tangential 

 wall-surface, in direct contact with the cytoplasm. The deposit may be formed in some Ferns 



Fig. 177- Cells of the endodermis, after Rumpf. i, from root ol Ophioglosstiiii vitlgatiini, 

 showing the Caspary-band in section, and in surface view, with pits, ii, from root of 

 Asplettiiun esculentiim, showing suberisation on the inner tangential wall, iii, from root 

 oi Matteticcia Siruthiopteris with suberisation [sH) deposited all round the inner surface 

 of the cell, but separated by the method of preparation. ( x 1000.) 



only on the inner tangential wall (Fig. 177, ii) : but in others it may be formed also on the 

 inner face of the wall, a condition which is stated to be general for the Phanerogams 

 (Fig. 177, iii). It has been demonstrated for the Schizaeaceae and Gleicheniaceae, and also 

 for the Cyatheaceae and Polypodiaceae. Thus it exists in certain Ferns which are rela- 

 tively primitive as well as in those which are more advanced. There is also a tertiary 

 condition of the endodermis common in Phanerogams, in which lignified deposits giving 

 mechanical strength are formed lining the endodermal cells internally. But this is not 

 known to occur in any of the Filicales. 



It is notable that the Caspary-zone of cell-wall is widest in plants with a primary type 

 of endodermis, as it is seen for instance in Ophioglossuin^ or H ehninthostachys (Fig. 173). 

 But it is narrower in those which have the secondary type, such as the Leptosporangiate 

 Ferns and the Phanerogams. It has been seen that the endodermis is a tissue structurally 

 isolated from those within and without. But there is some evidence that the cells of the 

 endodermis are in close relation with one another tangentially. This follows partly from 



