i)ixoN AND Ball — Channels of transport in Seedlings. 187 



sented in cross-section in fig. 7, PI. VIII. The sclerenchymatous sheath of each 

 bundle was largely developed, occupying about 75 per cent, of the area of the 

 cross-section. Sunken in the outer surface of this sheath, rows of small cells 

 containing siliceous spherules, as is common in palms and orchids, were observed 

 (2 and 13). 



The^ phloem and xylem within the sheath were normally developed, the 

 ratio of the areas of their cross-sections being on the average "about 6 : 5. The 

 vessels of the xylem having a diameter of 005-007 mm., were strengthened by 

 annular and spiral supports. The diameter of the sieve-tubes averaged about 

 0-01 mm., their length about 015 mm. In the specimen examined many of the 

 vessels contained a homogeneous slime-like substance. 



Here and there among the normally developed vascular bundles were found 

 greatly reduced bundles, consisting of one or two tracheae, and a very few' sieve- 

 tubes surrounded by a thick sheath of selerenchjonatous fibres. Often all the 

 woody elements, and even all the cellulose ones, were suppressed, and the bundle 

 consisted of fibres alone (fig. 2, PI. VII). These reduced bundles are probably 

 branches of the larger bundles, and end blindly in the fundamental tissue, as has 

 been described in the stem of Vanda teres (2). Their function appears to be 

 mechanical only. 



Above the constriction already noticed, the cotyledon expanded within the 

 seed to form the haustorium. Once within the seed, the cells of the superficial 

 layer presented a different appearance. They were isodiametrical, about 001- 

 003 mm. in diameter (figs. 12, 13, 14, PL X). Their walls were thin, their 

 cytoplasm largely vacuolated, and their nuclei conspicuous. They formed a 

 uniform layer of cells, following the lobed and papillose surface of the 

 haustorium, generally without discontinuities. On the distal surface of the 

 haustorium the superficial cells were somewhat smaller, and their cytoplasm 

 was less vacuolate. They stained more deeply. In this region they presented 

 somewhat the appearance of a columnar epithelium. 



Enclosed by this layer was the general mass of the haustorium, in the main 

 composed of thin-walled fundamental tissue, built of cells with rounded contoui"s, 

 which were smaller, and closely packed in the outer region. In the inner parts 

 of this tissue were enclosed large intercellular spaces, and the component cells 

 were formed like those of the spongy parenchyma of a leaf. The spaces in the 

 central regions were filled with air, but the smaller ones close to the surface 

 were often infiltrated by a slimy material resembling the debris of the 

 endosperm on the outer surface of the epithelium. This material appears, 

 during the growth of the haustorium, to force its way between the epidermal 

 cells into the intercellular spaces (fig. 12). In the specimen examined the 

 fundamental tissue was in many places traversed by the hyphae of the non-septate 

 mycelium of a fungus, which had developed subsequently to the opening of the 

 fruit, or possibly had established itself at some earlier stage. These hyphae, 

 being very rich in protoplasm and multinucleate, are easily distinguished from 

 the tubular cells which will shortly be described. The cells of the fundamental 

 tissue contained many starch grains, and smaller starch grains were occasionally 

 found in the superficial layer. 



The cells of the inner fundamental tissue are comparatively large, the 

 dimensions of their cylindrical branches being about 005 mm. X 010 mm. They 

 are often constricted where they come into contact with one another, and the 

 partition walls have wide pits. Here and there in this large-celled parenchyma 

 are to be seen giant cells, having about the same diameter, but a much greater 

 length, so that in one section they may show a length of 080 mm. or more 

 (figs. 3 and 4, PL VII). They are tolerably straight, and seldom branch. As 

 they pass between the other cells, they make contact with them. The areas of 



