286 THE JOURNAL OF INDIAN BOTANY. 



Gucurbitaceae, some Ficoideae, Bubiaceae, some Sola- 

 naceae, Scrophidariaceae, Nyctaginaceae, Amarantaceae, 

 Aristiolochiaceae and Euphorbiaceae, 



(d) or of a palisade tissue on both adaxial and abaxial sides in 



Gruci/erae, some Capparidaceae, Caryophyllaceae, Elati- 

 neae, some Zygophyllaceae, some Papilionaceae, Caesalpi- 

 neae, some Ficoideae some Composdtae, Salvador aceae, 

 some Asclepiadaceae, some Boraginaceae, some Convolvul- 

 .aceae, some Solanaceae, some Acanthaceae, and some PoZi/- 

 gonaceae, 



(e) or of a homogeneous short-celled palisade tissue in Menis- 



permaceae, some Capparidaceae, some Sterculiaceae, some 



Bhamneae, Bosaceae and some Bubiaceae, 

 if) or of palisade parenchyma round the vascular bundles in 



Portidaceae, some Ficoideae, Cyper aceae and Gramincae, 

 {g) or of palisade tissue on the upper side and of arm-palisade 



on the lower in most of the species with the exceptions 



that have been mentioned. 

 From the various modifications of the assimilatory tissue as 

 described above a process of evolution can be traced. The chloro- 

 phyll tissue formed of a homogeneous tissue of polygonal cells in 

 Gentianaceae and Filicinae mark the primary stage from which the 

 various higher stages can be said to have been developed, the assimi- 

 latory tissue formed of a homogeneous palisade tissue forming the 

 final stage of development. The arm-palisade tissue represents an 

 intermediate stage between the spongy tissue and palisade tissue. The 

 modification of tha spongy tissue into palisade tissue through an 

 intermediate stage of the arm-palisade tissue reduces the ventilating 

 system and consequently transpiration, towards which purpose all the 

 adaptations of desert plants are directed. 



The tendency of the chlorenchyma to develop into the palisade 

 tissue is further confirmed by the fact that in the axis, the assimila- 

 tory tissue when present, usually consists of arm-palisade cells or of 

 palisade cells. 



The arrangement of the palisade tissue in the form of girders 

 round the veins in Gyperaceae and Gramineae is quite adequate in the 

 leaf-blade which is characterised by an abundant articulation and 

 mechanical tissue. The assimilatory tissue in species of these orders 

 performs its own function and affords room for the development of 

 an articulation and mechanical tissue. 



In the centric leaves of Zygophyllaceae and Clienopodiaceae, the 

 assimilatory tissue forms more or less a sub-epidermal ring enclosing 



