88 CERATOPHYLLUM [CH. 



bottom of the water, weighted down with a "living freight of 

 aquatic molluscs, insects and annelids 1 ." The young shoots 

 formed in the spring, since they have not had time to become 

 so ballasted, rise erect in the water. The stems of the previous 

 year gradually decay away, and by the flowering time, in June 

 or July, they have practically disappeared. The fact that the 

 Hornwort, which has no surface layer of mucilage, becomes, 

 to so remarkable an extent, an asylum for aquatic animals, may 

 possibly be taken to afford some negative evidence for the 

 theory that the mucilaginous coat, which is almost universal 

 in hydrophytes, may have some value in preventing small 

 foreign organisms attaching themselves to the plant's surface. 



In addition to the normal leafy shoots, a second type of 

 branch is produced, which appears in some degree to take the 

 place of the absent roots (Fig. 57) 2 . These shoots, which are 

 described as * rhizoid-branches,' are whitish in colour and bear 

 leaves with extremely fine and delicate segments. Fig. 58 shows 

 the contrast between a rhizoid-leaf (A) and a water-leaf (5). 

 The rhizoid-shoots penetrate into the mud, where they pre- 

 sumably serve as anchors and absorbing organs. 



Although Cer atop hy Hum is not uncommon in northern lati- 

 tudes, there are certain indications that its birth-place may have 

 been in some more genial climate. Guppy 3 has shown, for 

 instance, that a very high temperature is required for the matu- 

 ration of the fruit. He noticed that in the drought of the hot 

 summer of 1893, the ovaries ripened well in a shallow pond 

 where the temperature of the water always rose above 80 Fahr. 

 (27 C.) in the afternoons, and occasionally as high as 95, 

 Fahr. (35 C.), while in the neighbouring waters, which were 

 not so much overheated, no fruits were produced. Curiously 

 enough, even in Fiji the fruit is only matured in the superheated 

 waters of shallow pools, tanks and ditches 4 . Conversely, the 

 vegetative organs cannot endure freezing, even for a period 

 so brief as to be quite harmless to many other aquatics; 



1 Guppy, H. B. (1894!). 2 Glttck, H. (1906). 



3 Guppy, H. B. (18941). 4 Guppy, H. B. (1906). 



