THE DEFENSIVE ARMOR OF PLANTS. 527 



by offering to snails full-grown leaves and young, tender ones of 

 the same grass. The latter will be taken and the others left. 

 But if, by a method of cultivation proposed by Sachs, we make a 

 normally siliciferous plant grow where it can get no silica, it will 

 be devoured at once. 



Some plants, that were avoided after treatment with alcohol as 

 well as before it, were found to contain a gum which the alcohol 

 failed to remove, and which stood between the snails and the edible 

 substance. Among these were linden, althea, cactuses, and gum- 

 my roots. Another series of plants, including an Arum,, narcissus, 

 leucojum, and the balsam touch-me-not, which contain no tannin 

 or gum or substances of disagreeable taste or smell, appeared to 

 be protected by raphides. Tabernsemontanus recognized in 1587 

 that the leaves of these plants produce a violent sensation of 

 burning in the bronchial tubes, and that it is not due to soluble 

 products or juices, but to the raphides, which are abundant in 

 their tissues. This is proved by the fact that the filtered juice of 

 the pounded leaves does not produce the burning sensation, while 

 the residue on the walls of the filter, and the pounded leaves them- 

 selves, produce the characteristic sensation that is felt after chew- 

 ing the fresh leaves. It is also confirmed by the fact that if the 

 leaves of Arum, maculatum, for example, are treated with dilute 

 hydrochloric acid, which dissolves the raphides, animals will 

 readily eat them, while they let alone leaves treated with alcohol, 

 even when they have been steeped in sugar-water. In the case of 

 the squill, snails avoid the outside of the scales, which are rich in 

 raphides, and eat the inner sides, which are free from them. So 

 in the narcissus and orchids, and various other plants, there are 

 parts protected by raphides which are objectionable to snails, and 

 other parts free from them that they eat. But, while raphides 

 protect against some animals, they do not against all. Birds and 

 ruminants do not object to the plants containing them ; and even 

 snails manifest different degrees of aversion to them. In a simi- 

 lar manner to these plants with raphides, some species of iris are 

 protected by crystals of oxalic acid. It is very probable that the 

 kinds of armor that we have named are available for protection 

 against other animals than snails. But investigation on this sub- 

 ject has not been sufficiently advanced to permit of definite con- 

 clusions or generalizations. 



Of the kinds of defense named, a minority of the plants stud- 

 ied by M. Stahl possess but one ; many are endowed with two ; 

 and some with three — as, for instance, Oxalis (oxalic acid, tannin, 

 and hairs) ; Circcea (bitter hairs, tannin, and raphides) ; Smilax 

 (thorns, raphides, and poisons) ; Aloe (leaf -teeth, raphides, and 

 bitter substance) ; and Pontederia (crystals of oxalate of lime, 

 raphides, and tannin). In fact, considering the number of ene- 



