INTERCELLULAR SECRETORY RESERVOIRS. - 443 



uninterrupted canals, there are between the vascular bundles short cylindrical sacs i™™ 

 or more in length, which are closed blindly at both ends. In the scale-like leaves of 

 many Cupressineae, as Thuja, &c., the passages are of course short, and relatively broad, 

 and may more properly be termed gaps or cavities. 



The passages and cavities of the leaves are continuous from the insertion of the latter 

 into the primary cortex, and there pass perpendicularly downwards. In the transverse 

 section they form a ring lying in the cortical parenchyma, and are generally grouped 

 according to. the arrangement of the leaves. At any rate in a large number of forms 

 they end blindly above the insertion of the lower leaves, without open communication 

 with other passages. Thus in the investigated Cupressineas with whorled leaves, as 

 Thuja, Biota, Juniperus. In J. communis e.g. a large passage enters the stem from 

 each leaf, and there runs downwards, in one of the three angles, to a point close above 

 the plane of insertion of the next lower whorl, and there ends. 



On the other hand, in Pinus sylvestris, Abies excelsa, and, according to jNIohl's state- 

 ments S in the Abietineae generally, the passages which come from the leaf, after descend- 

 ing through numerous internodes, open into others belonging to lower leaves ; the point 

 of confluence corresponds to a widening of the passage on which the higher one is inserted. 

 The passages of the primary cortex are therefore connected into a system of communi- 

 cating canals. The composition of this, as well as its distribution in individual forms, 

 remains to be more exactly investigated. 



The great majority of the Coniferae have no others in the primary tissues of the stem 

 besides the cortical passages above mentioned. This is the case in all investigated 

 Taxineae except Ginkgo ; most Cupressineae, Podocarpus, Cedrus, Abies, Tsuga, Pseudo- 

 larix. — Araucaria Cookii and Brasiliensis, and Widdringtonia cupressoides, have besides, 

 according to van Tieghem, a passage in the phloem of the primary vascular bundles, 

 which stops short before the exit of the bundle into the leaf. 



In the species of Pinus s. str., Larix, Picea, Pseudotsuga there is also a passage which 

 is not continued into the leaf, but it does not lie in the phloem, but in the xylem of the 

 primary bundles. 



Finally, Ginkgo biloba has large passages in the pith in addition to the cortical ones. 

 In transverse section there are one or two present, and so arranged that they correspond 

 to the insertions of the next higher leaves. Nevertheless they end blindly both down- 

 wards and towards the petiole, though the canal situated in the latter above the vascular 

 bundles lies in the ideal prolongation of the medullary canal situated opposite the leaf 

 in question. 



In the Root the passages of the primary cortex are wanting in all investigated Coniferae, , ; 

 and in most cases also those of the vascular bundles. In the latter, however, they are 

 found in certain species or groups; thus, according to van Tieghem, in Araucaria Cookii 

 and Brasiliensis there are five in each phloem portion of the diarch bundle, in Widdring- 

 tonia cupressoides one in the same position. The Cedars and Firs (Cedrus Deodara, 

 Abies pectinata, balsaminea, Brunoniana) and Pseudolarix Kampferi have a canal in the 

 middle of the radical bundle. In the Pines (Pinus s. str.) and Larix one passage lies 

 between the two shanks of each vascular plate, described on p. 357. 



AlismacesB and Butomeae. For Alisma Plantago Meyen, and especially Unger'^, have 

 given exact descriptions of the canals with milky contents, while Frank has cleared up 

 the history of their development. According to Unger's description the passages are 

 absent from the roots, but are distributed throughout the rest of the plant. In the 

 rhizome they traverse the parenchyma, forming a network branching in all directions, 

 and with a course independent of the vascular bundles. Those which enter the petiole 

 and peduncle branch off from this network, and then take a longitudinal course, being 



» Botan. Zeitg. 1859, p. 333. 



* Meyen, Phytotoniie, Taf. XIV.— Unger, Das System der Milchsaftgange in Alisma Plantago, 

 Denksch. d. Wiener Acad. Bd. XIII. 1857.— Van Tieghem, /. r. 



