BEVISION OF THE GENUS NAJAS. 391 



Size of the plant varying considerably, generally between 30 and 70 cm. A fruiting 

 specimen from Hickling Broad, gathered in September, was iO cm. long. 



Plants attached at the base of the stem and at the lower nodes of the shoots 

 by fibrous, often brownish-coloured roots. In the fresh state the stem and leaves are 

 extremely brittle, the former breaking at a touch or witli its owni weight when lifted 

 from the w^ater. 



Stem branching immediately above the base ; shoots generally creeping at the lower 

 nodes and ascending above. Internodes varying in length in different plants ; the lower 

 may be 6-12 cm. long ; in the same plant they become much sliorter from the base of 

 the shoot upward, becoming suppressed near the apex ; width varying (when dry) 

 from 1 to 15 mm. (in fresh specimens 2'5 mm.) ; number of spines very variable, often few 

 or none. Leaflo to 3'5 cm. long, often about 2 cm., 1 to 2'5 mm. broad. Teeth gener- 

 ally between 4 and 8 on each margin, though a much wider variation occurs ; consisting 

 of a conical outgrowth of the leaf-margin terminated by a strong, sharp-pointed, yellowish- 

 brown cell ; less than, greater than, or equal to the leaf- width ; 1 to 1 similar spines 

 occur on the back of the leaf. Sheath large and quite entire, or bearing on each of its 

 rounded shoulders a very small tooth or one prominent tooth, which may be followed 

 from above downward by one or a few smaller teeth, or there may be more than one 

 prominent tooth or several inconspicuous ones ; teeth ending in a sharp, yellowish, spiny 

 cell; fertile sheaths generally very asymmetrical. Intravagiual scales varying much in 

 shape on the same plant ; generally about 6 mm. long, and tapering more or less obliquely 

 from a broader base. 



Male flower 3 to 4 mm. long; anther when young completely enveloped in the spathe 

 and perianth, the cells of wdiich contain a bright red sap ; before dehiscence the short 

 stalk grows and the flower is pushed through the spathe, which liecomes split laterally ; 

 the perianth becomes torn, and the anther dehisces from above downward. Female 

 flower when mature about 3*75 mm. long, the ovary occupying about one-third of the 

 whole length ; when three stigmas are, as usual, present, one is often smaller than the 

 others. Fruit 4 to 8 mm. long, generally about 5 mm. ; usually ellipsoidal or more or 

 less ovoid, becoming narrowed at the top, where it bears the withered style and the 

 remains of the stigmas ; pericarp in fresh specimens turgid and succulent, but wiien 

 dried thin and membranous ; it is finally split by the growth of the seed, which is of a 

 similar shape. 



The general habit shows a wide variation, depending upon the length of the internode, 

 the absence or presence of spines and their number, the greater or less rigidity of the 

 leaves, their length and breadth, and the size and number of their marginal teeth. The 

 size and shape of the fruit also vary considerably. The study of a large series of 

 specimens reveals a number of forms which bear certain relations to geographic distribu- 

 tion, though doubtless largely determined by local conditions, such as depth of w'ater, 

 presence or absence of a current, strength of current, presence of salt, or temperature. 

 As we might expect, these forms pass more or less one into another. I have purposely 

 avoided attaching names to the following, which are fairly easy to distinguish : — 



a. A luxuriant form with internodes much elongated and unarmed, or, especially the 

 shorter upper ones, sparsely toothed. The leaves, which are uniformly linear or narrowing 



