AND IRRITABILITY OF SENSITIVE PLANTS 217 



stipules. In the stem the crystal cells become more diffuse near the 

 beginning of the primary root, and are entirely wanting in the root 

 endodermis. 



The regularity in the shape of the individual crystals, the extensive 

 distribution of crystals throughout the plant, the distinct protoplasmic 

 sheath around each crystal, intercellular connections between the 

 crystal cells, contact of some of the crystals with the dividing cell walls, 

 all these show a decided advance in cr>'stal relation over the plant pre- 

 viously described. 



Mimosa Spegazzini 

 Of the species of Mimosa that have been studied, M. Spegazzini 

 shows the most highly specialized irritabiUty. It is slightly more 

 sensitive than Mimosa pudica in that the different phases of a stimula- 

 tion act are slightly shorter than for the latter species. Twenty to 

 thirty pairs of secondary leaflets are borne by each of the two leaflets. 

 Primary, secondary and tertiary puh'ini are well developed. Rather 

 strong hairs are developed on the entire plant. 



The nyctitropic movement of the leaves is very similar to that of 

 Mimosa pudica. The secondary leaflets move upward and forward,, 

 the midribs converge and the whole leaf drops about 90 degrees (Plate 

 LXI, Fig. 12 and 13). 



When a mechanical stimulus, such as a forceps pinch, is applied to 

 one of the terminal secondary leaflets after a latent period of less than 

 \i second the leaflet stimulated rises and its partner almost at the 

 same time. The stimulus is then carried down the midrib, the pairs 

 of secondary leaflets closing in order; in 9 seconds all the secondary 

 leaflets have closed, the midribs converge followed in 3 seconds by a 

 drop of the entire leaf. The stimulus moves up the other leaflet with 

 the result that the secondary leaflets close in order. In 20 seconds after 

 the stimulus had been appUed all the secondary leaflets are closed. 

 The stimulus is propagated through the stem to other leaves. The 

 writer in one case observed that five leaves above the one stimulated 

 and three below dropped. The extent of propagation of stimuli through 

 the stem is a decided advance from the irrito-contractile view point 

 over that of Mimosa pudica. 



In crystal distribution the relation in M. Spegazzini is almost exactly 

 parallel with that of M. pudica. The crystals are of the same type, 

 of the same relative size, are present in leaflets, stipules, petioles and 

 stem, but not in the pulvini. The chief difference between the two 



