276 SUMMARY OF CURRENT RESEARCHES RELATING TO 



pendent foliar structures, not resulting from the union of two different 

 organs ; in the young condition therefore the cone of Coniferse must 

 be regarded as a single flower and not as an inflorescence. With 

 regard to the origin of the swellings on these leaves, investigation 

 shows that either only one cushion is formed on the carpel, which is 

 then always on the upper side, or that the swelling takes place on 

 all sides. In the Cupressinese a partial transformation of the other- 

 wise parenchymatous structure of the carpels always takes place 

 into scattered sclerenchymatous cells. 



In the Abietinese the structures formed in the axils of the carpels 

 must be regarded as placentae; and here also each cone must be 

 regarded as a single flower, and not as an inflorescence. These 

 placentae always appear at first as axillary swellings, and afterwards 

 as transverse cushions in the axil of the carpels which generally 

 remain small. In this condition they are nearly alike in the different 

 species, and only subsequently develope in different ways. The 

 rudimentary cones attain a very different degree of structure in the 

 different species in the autumn preceding their true development. 

 In the species of Larix, and in Pinus sylvestris and montana, there is 

 to be met with at that time only a longish oval mass of tissue, the 

 subsequent axis ; while in Tsuga canadensis not only have the carpels 

 begun to be formed, but even the placentae in their axil. 



Structure of the Leaves and Stomata in Coniferse.* — Dr. A. 



. Mahlert has examined in great detail the anatomy of the leaves 



and the structure and mode of development of the stomata in a large 



number of Coniferae, and in a few Cycadeae and Gnetaceae. The 



following are the general results arrived at : — 



In most Coniferse the stomata are recognized on the white or grey 

 coating of wax, which also extends into their outer opening. This 

 coating is altogether wanting in Taxus, Taxodium, Gingko (Salis- 

 huria), Torreya, and Sciadopitys, and is but very feebly developed in the 

 broad-leaved Araucarias, Dammara, and some species of Podocarpus. 



In GingJco, Araucaria Cunningliamii, A. excelsa, A. CooMi, Crypto- 

 meria, Arthrotaxis, and nearly all Cupressineae, the stomata are 

 distributed without order over the surface of the leaf. In Dammara, 

 Taxodium, Araucaria imhricata, A. hrasiliensis, A. Bidwillii, Cunning- 

 hamia, and Sequoia, the longer axes of the stomata are parallel to one 

 another, in the two first usually at right-angles to the direction of 

 the vascular bundles, in the rest parallel to it. In Pinus, Picea, 

 Cedrus, Larix, Abies, Tsuga, Pseudotsuga, Saxe-Gothea, Taxus, 

 Cephalotaxus, Torreya, Sciadopitys, and Podocarpus, they are in 

 longitudinal rows, parallel to the vascular bundles. Three different 

 forms of guard-cell are described and figured. 



The epidermal cells are nearly always lignified and thickened on 

 the outer side ; beneath them is a hypodermal bast-layer, the cells of 

 which are lignified, and lengthened in the longitudinal direction of the 

 leaf. A few cases of exception to both rules are given. 



* B(.t. Centralbl., xxiv. (1885) pp. 54-9, 85-8, 118-22, 149-53, 180-5, 214-8, 

 243-9, 310-2 (2 pis.). 



