AND IRRITABILITY OF SENSITIVE PLANTS 199 



of the leaves of certain members of these families will be taken up in the 

 succeeding chapters. The plants studied include forms that are feebly 

 sensitive, others that are sensitive to a marked degree, and others that 

 are very highly sensitive. 



A very suggestive feature of histological interest in the Leguminosae 

 and the Oxalidaceae is the presence of crystals. These are found in 

 practically all members of these families. In the individual plant they 

 are present in leaves and stems. 



The writer made a careful study of the crystal distribution in the 

 different sensitives, from forms that are scarcely sensitive to those that 

 exhibit the most specialized t>T3es of sensitivity. 



Plant crystals have long been known and studied. Malpighi (32) 

 was the first to observe "crystal clusters" in plants. 



Von Leeuwenhock (23) noted several forms of crystals and described 

 these briefly. 



Scheele (41) was the first to make a chemical investigation of plant 

 crystals, and indicated that they are composed, for the most part, of 

 calcium oxalate. 



These earlier investigations of crystals were made on plants not 

 included in the families here studied. 



Meyen {33) was probably the first one to study rather carefully the 

 crystals found in the cortex of the stem of Robinia pseiidacacia. The 

 crystals were studied from the chemical standpoint. He agreed with 

 Scheele that the crystals are composed of calcium oxalate. Meyen 

 observ^ed that the crystals are always contained in cells, and not in 

 intercellular spaces, as the preceding workers beheved. In this work 

 no reference is made to the distribution of crystals, but their forms and 

 shapes are described. 



Holzner (21) takes up a general study of crystals, with brief reference 

 to those of Robinia pseudacacia. This work is rather important in 

 that it includes a summary of all the literature on crystals up to 1864. 

 Poulsen (38) briefly describes the crystals found in various papiliona- 

 ceous plants, such as Apios, Phaseolus and Dolichos. In these, accord- 

 ing to Poulsen, crystals are especially abundant in the characteris- 

 tically swollen bases of the petioles (pulvini) and in the thickened 

 flower stalks. They are not found in the epidermis but in the parenchy- 

 ma tissue beneath, in the parenchyma cells of the fibro- vascular bundles 

 and in the central pith-like tissues. Those in Phaseolus, he says, are 

 large, single crystals which have no definite relation to the axis of the 

 organs. They are elongated, prismatic, rhombic in cross section, and 



