A. B. Rendle. — Najadaceae. 



Fig. 2. N. horrido, A. Br. Caulis transverse 

 sectus. (See. Rendle). 



generally furnished with small teeth or longer spine-bearing fimbriae; the tooth or fimbria 

 always ends in a sharp yellowish-brown spine. 



The form of the sheath is generally constant for individual species and often for lar<*er 

 groups. Sometimes as in N. indica it shows wide differences even on the same plant. 



Inside the sheath at the base arises a 

 pair of minute hyaline cellular scales ; these 

 are often subulate or filiform, but their 

 shape is very variable even on the same 

 plant, They oeeur in the cotyledon. 



The lamina forms an obtuse angle with 

 the sheath. It is generally narrow linear in 

 outline tapering above, sometimes becoming 

 filiform ; it is rarely broader and linear-lan- 

 ceolate as in some forms of N. marina. The 

 margin varies considerably. In the broader- 

 leaved forms of N. marina it is sinuate- 

 dentate, the teeth often being longer than 

 the leaf width, and ending in a strong 

 yellow-brown spine with a base of several 

 supporting cells. There is every gradation 

 between this and the strueture in JV. gra- 

 minea, where simple marginal cells protrude 

 in the form of ascending yellow-brown 

 translucent spines visible only under a lens, 

 the leaf-margin appearing quite entire to 

 the naked eye. In N. marina and several of its varieties , teeth similar to those on the 

 internodes are found on the midrib on the back of the leaf. Similar dorsal spines oeeur in 

 N. laeerata. As A. Braun indicated, the size and strueture of the marginal teeth afford 

 useful specific characters. 



Anatomy (Anatomische Verhältnisse). The internal strueture of stem and leaf is 

 very simple. The greatest differentiation oecurs in N. marina where we find in the stem a 

 definite small-celled epidermis, a many-layered parenehymatous cortex in which is a row of 

 intercellular Spaces, and a slender central cylinder. The stele is bounded by a layer which 

 shows endodermoid thickenings on the radial walls, and consists of narrow closely packed 

 thin-walled cells surrounding a central cavity. Just below the growing-point this cavity is 

 oecupied by thin elongated cells which doubtless represent tracheal elements. In the leaf of 

 JSf. marina a definite epidermis surrounds a large-celled mesophyll consisting only of a 

 single layer at the edges, becoming two-layered as we advance inward, and separated 

 towards the middle line on each side by a large intercellular space. A slender stele similar 

 to, but smaller than that of the stem runs up the middle line, and is surrounded by one or 

 two layers of mesophyll-cells. 



The remaining species forming the subgenus Caulinia, are even simpler in strueture. 

 In the stem an epidermis closely resembling the underlying cortical layer surrounds a cortex 

 consisting generally of one or two outer layers , which is connected with an inner layer 

 surrounding the stele by slender bands separating large intercellular Spaces; the connecting 

 bands are for the most part only one cell thick. In Najas horrida (Fig. 2) we find a more 

 substantial cortex approaching that typical of N. marina. The leaves, which show some 

 Variation in strueture, consist generally of two layers separated at a greater or less distance 

 from the midrib by a larger or smaller intercellular space. Single cells, or groups of a few, 

 in various positions may form thickened fibrous supporting cells; these may be constant for 

 a given species or on the other hand variations may oeeur within its limits. The longitudinal 

 intercellullar spaces in the leaf are interrupted by transverse septa to the strong develop- 

 ment of which are due the horizontal lines running from the midrib towards the margin, 

 which are characteristic of some species and oeeur on older leaves in others. 



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