192 Scientific Proceedings^ Royal Dublin Society. 



cell, and therefore must pass through the protoplasmic lining of the cell. Con- 

 sequently, unless we regard the cells lying next to the vessels as being relatively 

 more impermeable, there seems to be no clifficulty in understanding how organic 

 substances can be injected into the vessels. 



On the other hand, the living cells of the vascular bundles seem ill-adapted 

 to the task of translocation. The sieve-tubes are late in development, and even 

 when fully formed would offer a greater obstruction to diffusion than would 

 the storage tissue, which, in addition to a large cross-sectional area, is better 

 provided with pitted cell-walls. 



With a view to obtaining some evidence on the normal course of the current 

 in the xylem of the cotyledons, the following experiments were conducted : — 



A seedling of Vicia faba, with a root -SS cm. long, was used. The cotyledons 

 were cut across in a direction parallel to the direction of the root, and the cut 

 surface was placed under a solution of .eosin. The root vtas surrounded with 

 moist Sphagnum moss. iVfter twenty- four hours all the bundles of the cotyledons 

 were injected with eosin, and traces of eosin were found in the root down to 

 about 1-5 cm. below the origin of the plumule. During this period the root had 

 elongated 05 cm. 



In another experiment a seedling with a shoot 12 cm. and a main root about 

 20 cm. long was used. The root was cut across and immersed in an eosin 

 solution for one and a half hours, and at the end of that time the whole of the 

 wood in the cotyledons was deeph' injected with eosin. 



Such experiments, unfortunately, give no indication of the normal course of 

 the current in the wood. They do show, however, that if water or a solution of 

 eosin can be drawn into the plant at any i^oint it will be transported with an 

 equal facility in an upward or downward direction, according to requirements. 



That the cotyledons have the power of absorbing water is shown by the 

 rapidity with which the dry seeds swell up when immersed in water. It seems 

 probable, therefore, that water continually passes in through the cotyledons 

 during germination ; and, unless the cells lying next to the vessels are specially 

 impermeable, a solution of organic substances would travel by means of the 

 wood from the cotyledons in the direction of the growing points. 



Summary. 



1. In the seedlings of the palms examined there is a network of vascular 

 bundles close below the absorbent surface of the haustorium, which is embedded 

 in the endosperm. This network is connected with the growing embryo by 

 bundles which traverse the basal parts of the haustorium and the petiole 

 longitudinally. 



2. Well-developed xylem, consisting largely of lignified tracheae, is found in 

 the vascular bundles of "organs connecting embryos with their stores. 



3. Sclerenchymatous sheaths and cords of sclerenchymatous fibres are also 

 often found in these organs. These sclerenchymatous elements are not continued 

 into the haustoria. 



4. The total area of the cross-section of the phloem of all the bundles in the 

 haustoria is much greater than that of the bundles in the connecting organs or 

 petioles. There is not the same disproportionality in the cross-section of the 

 xylem in the two organs. Sometimes the total area of the cross-section of the 

 xylem of the bundles of the petiole approximately equals that of the bundles of 

 the haustorium, e.g., in Phoenix dactylifera. 



5. In Vicia faba tracheal elements are differentiated in the petiole much 

 earlier than are sieve-tubes. Before the latter appear, considerable transport 

 of organic substances to the embryo must take place. 



