SCIENCE-GOSSIP, 



[Maech 1, 1865. 



merely cells combined in several varieties 

 of texture. Now, theorists assume the 

 primary form of cells to be spherical— nature 

 or vital defects in nature (i.e., in growth or 

 development) occasioning deviations, and 

 also causing modifications of the cell where 

 some particular end of plant life is to be 

 accomplished. Thus it is that woody fibre 

 comes to consist of elongated cells thickened 

 by secondary deposits so as to attain great 

 tenacity ; and thus also that the ducts and 

 spiral vessels of the vascular tissue, and the 

 peculiar vessels of plants having a milky sap, 

 are cells of special modification, in v/hich the 

 adjoining tubes have often free communica- 

 tion with or run into one another. Indeed, 

 the ultimate results of vegetation, the fruits 



EiG. 1. Pig. 3. 



of the earth, may be separated into leaf-masses 

 and resolved into cellular modifications. Thus 

 the dicotyledons give, as everyone knows, 

 two seed lobes, or actual seed leaves in 

 germination, as in the case of the pea (fig. 1) ; 

 whilst the monocotyledons, represented by the 



Fig. 3. Eig.4. 



exaggerated section of oat (fig. 2), exhibit the 

 rudimentary forms of futiu'e leaves. In the 

 leaf itseltj whether we take the curved or 

 divergent venation of endogen (as in figs. 3 



and 4), or the netted venation of exogen (as 

 in fig. 5), we can see, through the outer 

 cuticle or skin, the veins ramifying through 

 the inner portion or parenchyma ; and 

 botanists all admit these to be modifications 



EiG. 5, 



Fig. 6. 



of the cell — the veins in the first instance 

 (fig. 3) running parallel to one another from 

 end to end of the leaf ; in the second instance 

 (fig. 4) they ai-e given off from one principal 

 vein or midrib ; and in the last case (fig. 5) 

 constitute a complicated net-work of nume- 

 rous branches and branchlets. The parallel 

 venation will be found in the leaves of lilies, 

 palms, bananas ; the netted, in those of oaks, 

 beeches, &c.'" The most remarkable modifi- 

 cations of the leaf-type are probably the 

 Indian cups (Sarracerda) of ISTorth America, 

 and the still more elegant shapes of the 

 pitcher-plant {N'epenthes) (fig. 6). Some- 

 times, as in Gloriosa sujoerha, the midrib, 

 which, as shown above, is in fact the principal 

 vein of the leaf, becomes lengthened out into 

 a tendril. The tendrils in the vine proceed 

 from the lateral leaf-buds ; those of the 

 passion-flower from the terminal ; whilst the 

 solitaiy thread-like attachment of the cucum- 

 ber leaf is a sort of stipule, the stipules being 

 leaf-like organs situated on either side of the 

 point at which the leaf is attached to the 

 stem. The pea and vetch having compound 

 leaves, the tendril is formed of the end of the 

 common footstalk, whilst in the vanilla-plant 

 the whole leaf is sometimes elongated into a 

 tendril. 



If v.'e notice the arrangement of leaves on 

 the stems of plants, we will find that it pro- 

 ceeds invariably in a spiral — a favourite mode 



* Amongst monocotyledons, Arum, Calla, Lilium 

 giganteum,"kQ,., are considered exceptions to the 

 general rule, from liaving netted venation; and 

 amongst dicotyledons, Neretim, &c., from having 

 parallel. 



