ll'Z 



MORPHOLOGY OF TISSUES. 



them they run into the cortex and pith, forming, especially in the nodes of the stem 

 and the cushions of the leaves, numerous ramifications. Still more similar to the 

 bast-fibres are the laticiferous vessels of the Asclepiadae and Apocynaceae ; some are 

 pointed at both ends ; sometimes also they have, like them, thickened and character- 

 istically striated walls ; they are found sometimes actually in the place of true bast- 

 fibres, sometimes united with them into one bundle (of the phloem), or surrounding 

 them. In these cases it is therefore by the presence of the latex that the rela- 

 tionship of these metamorphosed bast-elements to true laticiferous vessels is esta- 

 blished; the more milky their contents, the thinner becomes the wall (Hanstein, /. c. 

 p. 2 1). Together with these simple fibre-like tubes, branched and anastomosing ones 

 are, however, also found, especially in the nodes of the stem, the pith, and the cortex 

 {Nerium Oleander). In the Aroideae laticiferous vessels united into a network occur 

 in the fibro- vascular bundles and the fundamental tissue ; but some genera, as Caladium 

 and Arum, exhibit the peculiarity of laticiferous tubes running within the xylem, 

 which, from their position and partly from their structure, must be considered as 

 metamorphosed spiral vessels ; but in the fundamental tissue there also occur simple 

 broad tubes similar to these. In the genus Acer the sieve-tubes are transformed into 

 laticiferous vessels, as is inferred from their position in the phloem and the structure 

 of their walls. 



The vesicular vessels discovered by Hanstein in species of Allium resemble sieve- 

 tubes in form if not in position ; they contain (evidently at least in the bulbs of 



A. Cepa) latex, and in some other respects resemble 

 the more simple laticiferous vessels of Dicotyledons. 

 They consist of long broad cells which touch one 

 another at their broad ends and there have sieve- 

 like or latticed septa ; where two vessels are in lateral 

 contact, the longitudinal walls have also a pitted 

 structure similar to the sieve-tubes (Fig. 95); the 

 perforation of the septa, /. e, the formation of open 

 pores, is, however, doubtful in the species of Allium. 

 These vesicular vessels permeate the scales of the 

 bulb; at their base they anastomose, like those 

 of the foliage - leaves and flower-stalks, into long 

 nearly parallel rows, which are generally separated 

 from the epidermis by 1-3 layers of cells. Similar 

 rows are formed by the vesicular vessels of Amaryl- 

 lideae (Narcissus, Leucojum, Galanthus) ; they re- 

 semble, however, the laticiferous vessels in this, 

 that the septa of the rows of cells become partially, 

 sometimes entirely, absorbed ; but their latex is not 

 milky, and contains numerous needle-like crystals 

 of calcium oxalate (raphides). To these must be 

 added numerous other structures in Monocoty- 

 ledons which bear scarcely any other resemblance 

 to laticiferous vessels ; in some genera of Liliaceae 

 (Scilla, Ornithogalum, Muscari) the vesicular vessels 

 often form shorter interrupted rows of cells, and 

 in the bulbs themselves larger isolated paren- 

 chyma-cells, similar to the former in containing raphides. That the cells containing 

 raphides can, however, actually unite into tubes, which morphologically altogether 

 resemble laticiferous vessels, is shown in the Gommelynaceae. Here rows of cells which 

 are early distinguished from those which surround them by containing raphides arise in 

 the young parenchyma of the fundamental tissue of the internodes and leaves ; they no 

 longer divide ; while their neighbours continue to become shorter by septa, they remain 



Fig. 95.— Longitudinal section through the bulb- 

 scale of Alliitni Cepa; e the epidermis ; c the cu- 

 ticle ; / parenchyma ; sg the latex of the vesicular 

 vessel coagulated by solution of potash ; ^r ^r its 

 septum ; the longitudinal wall exhibits a pitted 

 structure ; it separates the vesicular vessel, in this 

 case very visible, from one lying behind it. 



