ZOOLOGY AND BOTANY^ MICEOSCOPYj ETC. 73 



Laticiferous Vessels,* — D, H, Scott has investigated the struc- 

 ture and development of the laticiferous vessels, chiefly in Tro.grypo'jrjn 

 eriospermus ; also in Scorzonera hispanica, Taraxacum officinale, and 

 Chelidoniiim majus. The following are the most important results : — 



The laticiferous vessels are developed out of rows of cells, the 

 transverse walls of which have been gradually absorbed, and, when 

 two vessels lie side by side, the lateral walls also partially. The 

 resorption usually takes place at an early period ; in seedlings during 

 the first stages of germination ; in the secondary cortex shortly after 

 the cells in question have separated from the cambinm. 



The connection between distant laticiferous vessels is brought 

 about in two ways ; either by rows of cells that run transversely 

 coalescing with one another, or by protuberances which unite in their 

 growth, and which finally form canals similar to those of the Conjugatse. 



Even before the first septa are absorbed, the cells are characterized 

 by special contents, of which latex is probably a constituent. 



Epidermal System of Eoots.f — L. Olivier has made a careful 

 study of the epidermal tissue in the roots of Vascular Cryptogams, 

 Gymnosperms, Monocotyledons, and Dicotyledons, dividing the Latter 

 into two classes, those in which the secondary vascular system 

 originates early, and those in which it originates late. The following 

 are the general results : — 



The piliferous layer of the root does not correspond to the 

 epidermis of the stem, but rather to one of its hypodermal layers. It 

 is this which gives birth to the " veil," a system of layers of cells 

 proceeding from the piliferous layer ; as it peels off, the subjacent or 

 epidermoidal layer most generally assumes the anatomical character 

 of the epidermis, and the same physiological functions. 



The secondary tissue of the epidermal system of the root is 

 either parenchymatous or of a corky nature. The secondary epidermal 

 parenchyma proceeds from a peripheral layer of the central cylinder ; 

 it attains considerable development in Dicotyledons with early secon- 

 dary vessels, and in Gymnosperms ; there is none in Vascular Cryp- 

 togams, in the great part of Monocotyledons, nor in Dicotyledons with 

 late secondary vessels. 



In Gymnosperms and in Dicotyledons with deciduous primary 

 bark, the cork is derived from the pericambial layer. It is composed 

 of tabular cells, the radial walls of which are very short. 



In woody Dicotyledons with late secondary vessels, in Monocoty- 

 ledons, and in Vascular Cryptogams, the production of cork takes 

 place in the external zone of the cortical parenchyma ; the cork is 

 here composed of cubical cells. 



In any particular species, the zone of the root where the cork 

 appears depends on the transverse diameter of the organ, and on its 

 physical surroundings. The diameter being the same, the cork is 

 generally earlier and more abundant in the aerial than in the under- 

 ground roots. 



* Scott, D. H., ' Zur Entwickelungsgeschichte der gegliederten Milchrohren 

 der Pflanzen.' Inaugural Dissertation. 23 pp. Wiiizburg, 1881, 

 t Ann. Sci. Nat. Bot., xi, (1881) pp. 5-129 (8 pls-)- 



