318 HOW CROPS GBOW. 



ingredients essential to growtli. The hard, dense coat of 

 the seed of the common weed "stone-crop" {Lithosper- 

 mum) usually contains some 13 to 30 per cent of silica 

 and twice that amount of calcium carbonate. Hohnel 

 produced these seeds in water-culture from well-grown 

 plants deprived of silica and found them quite normally 

 developed. The seed-coat was permeated with calcium 

 carbonate, which appears to have fully replaced silica 

 without detriment to the plant {Haberlandt, Unter- 

 suchungen, II, p. 160). 



Chlorine. — As has been mentioned, both Nobbe and 

 Leydhecker found that buckwheat grew quite well up to 

 the time of blossom without chlorides. From that 

 period on, in absence of chlorides, remarkable anomalies 

 appeared in the development of the plant. In the ordi- 

 nary course of growth, starch, which is organized in the 

 mature leaves, does not remain in them to much extent, 

 hut is transferred to the newer organs, aad especially to 

 the fruit, where it often accumulates in large quantities. 

 In absence of chlorides in the experiments of Nobbe and 

 Leydhecker, the terminal leaves becam. thick and fleshy, 

 from extraordinary development of cell-tissue, at the 

 same time they curled together and finally fell off, upon 

 slight disturbance. The stem became knottyj transpira- 

 tion of water was suppressed, the blossoms withered 

 without fructification, and the plant prematurely died. 

 The fleshy leaves were full of starch-grains, and it ap- 

 peared that in absence of chlorine the transfer of starch 

 from the foliage to the flower and fruit was rendered im- 

 possible ; in other words, chlorine (in combination with 

 potassium or calcium) was concluded to be necessary to 

 — was, in fact, the agent of — ^this transfer. 



Knop believes, however, that these phenomena are due 

 to some other cause, and that chlorine is not essential to 

 the perfection of the fruit of buckwlieat (see p. 196). 

 Knop {Chem. Centralhlatt, 1869, p. 189) obtained some 



