Dr. AUemao on the Origin of Vessels in Plants. 215 



which are the first vessels formed, derive their origin in the stem 

 from the vital point in which the leaves originate, whence they ascend, 

 forming bundles in the leaves, of which they constitute the nen^ures, 

 and whence they descend through the stem to form the medullary 

 sheath. Secondly, that roots do not exist in the embryo, but are 

 formed in the young plant when, freed from its seminal envelopes, it 

 penetrates the earth. [This is, however, subject to some exceptions 

 in cases where the roots begin to sprout while contained within the 

 seed.] The radicular bulb which is destined to produce them bears 

 some analogy with the gemmule, and may be considered as a primary 

 spongiole, through which the plant absorbs nutriment prior to the 

 production of roots. Thirdly, that the fibrous, ligneous or reticu- 

 lated vessels are formed posteriorly to the appearance of the tracheae, 

 their origin being at the vital point from which the roots proceed, 

 whence they ascend in bundles through the stem until they reach 

 the extremity of the nervures of the leaves, being always external to 

 the tracheae, and whence they descend through the root as far as the 

 extremities of its ramifications, leaving almost always in its centre a 

 kind of canal filled with cellular tissue, which is a true pith, and com- 

 municates with the herbaceous envelope by means of medullary rays, 

 but is not enclosed by tracheae in dicotyledonous plants. Tracheae 

 are to be found, however, in the roots of nearly all monocotyledonous 

 plants, or if absent, their place is supplied by mixed or scalariform 

 vessels. In this exposition of his views Dr. Allemao has gone beyond 

 what appears on the face of the drawings sent, and has, he is aware, 

 repeated several well-known facts : what he believes to be new in 

 them is the extension of two vascular systems in opposite directions, 

 and their increment at their respective extremities ; in other words, 

 the projection upwards and downwards of fibres or vascular bundles. 

 Fourthly, that the radicular branches, as appendicular or radiated 

 organs, are in their origin perpendicular to the fibres of the stem, 

 and not continuous with them, contrary to the theory maintained 

 by Gaudichaud. 



The same facts are demonstrated in monocotyledonous plants by 

 microscopical observations on the young rooting bulbs of Fonrcroya 

 gigantea. A longitudinal section passing through the centre of the 

 bulb shows, on repeated and careful dissection, that the bulbous 

 mass is formed of rather dense cellular tissue filled with a viscous 

 lymph, the cells of which contain much fecula and a large quantity 

 of raphides or solitary prisms. Of the numerous sheathing and con- 

 centric leaves, the central one. in its earliest development, is com- 

 posed only of very fine cellular tissue ; the one next in succession 

 outwards is still cellular, but beginning to receive tracheal ramifica- 

 tions, which are the upper extremities of numerous simple tracheae 

 forming a crown around the vital point which Dr. Allemao regards 

 as the limit between stem and leaves. These tracheae are very 

 slender, vermicular or fusiform, with a curvature in the middle, the 

 convexities of which look towards the centre ; extending upwards 

 they penetrate the leaves in great number running parallel to each 

 other, and passing downwards they cross and become external to 



