355 
the Leaf of Welwitschia mirabilis. 
to the long axis of the leaf. They arise lysigenously owing to deliquescence 
of certain mesophyll cells. Similar mucilage canals occur in all parts of 
plants, except in a very young seedling. According to Hooker ( 9 , p. 12), 
even spicular cells are sometimes included in the contents of the canal. 
General Conclusions and Summary. 
It would not be advisable to draw 7 phylogenetic conclusions from the 
anatomy of the leaf only. Yet there are not a few important points which 
exhibit the typical Gymnospermic characters, and especially show a close 
relationship to other members of the Gnetales. 
The paired bundles in the cotyledon, the leaf (here the primary bundles 
alone should be taken into account), and in the bracts, 1 which are derived 
from the ‘double leaf-trace’, are worthy of notice. The paired bundles 
are to be seen in the leaf and bract of Ephedra , whereas in Gnetum this 
point is of more Angiospermic character. 
The leaves are always opposite and decussate in these three genera, 
although tricyclic leaves sometimes occur in Ephedra. 
Cyclic leaves are not known in any other group of Gymnosperms except 
in Cupressineae and in Araucarineae (Dammar a). 
It has been pointed out that the base of the cotyledons in Welwitschia 
is connate. The connate leaf-base is to be seen in the leaves and bracts of 
these three genera. In Gnetum the leaves are very slightly connate, so 
that this character is not clearly comprehended in an older stage. 
The structure of the stoma is also on the whole similar in all these 
genera. The development of the stoma is very much the same in 
Welwitschia and in Gnetum ( 22 ). 
The hypodermal sclerenchyma with unlignified wall is present in these 
three genera. 
One of the interesting features is the occurrence of crystals and granules 
of calcium oxalate in the cell-wall of various parts of the plant, such as the 
epidermis ( 16 , p. 541 ; 4 , p. 102) and mesophyll ( 16 , p. 521 ; 4 , pp. 141, 
335) of the leaf, in the spicular cell ( 16 , p. 52 7 ; 4 , p. 133), in the epidermis 
(1, p. 14) and parenchyma ( 16 , p. 521) of the stem, and in the soft tissue 
of the root. This character prevails in Conifers 2 and very seldom occurs 
1 A detailed account of morphology of the bracts will be dealt with in a special paper. 
2 I have observed myself this phenomenon in various parts of the following plants : i. Spicular 
cells with crystals in Araucaria imbricata (leaf and pith), Acmopyle Pancheri , Dammara australis , 
Fokienia Hodginsii , Sciadopitys verticillata (leaf), Torreya calipornica and T. taxifolia (cortex). 
2. Crystals deposited in the cortex (in the widest sense) of Araucaria imbricata , Callitris rhomboidea , 
Fitzroya patagonica , Juniperus co?nmunis, Libocedrus decui'rens, Saxe-Gothaea conspicua , Sciadopitys 
verticillata , Taxus baccata, Thuja sp., Torreya calif arnica, T. taxifolia, Wellingtonia gigantea, and 
Widdringtonia cupressoides (also cf. 16). 3. In pith of Araucaria imbricata, Saxe-Gothaea con- 
spicua, and Torreya calipornica. 4. In the outer wall of the epidermis of certain species of the 
following twenty-nine genera : Abies, Acmopyle, Actinostrobus, Athrotaxis, Callitris, Cedrus, Cepha- 
lotaxus, Cryptomeria, Cunninghamia, Cupressus , Dammara , Fitzroya, Fokienia, Glyptostrobus, 
funip>erus, Libocedrus, Phyllocladus , Picea, Pinus, Prumnopitys , Pseudotsuga, Sequoia , Sciadopitys , 
Taiwania, Taxodium, Taxus, Tetraclinis, Tsuga, and Widdringtonia. 5. In chlorenchyma of all 
known coniferous genera except Larix and Pseudolarix, where 1 have failed to detect any trace cf 
this substance, probably being due to my material. 
