146 MINNESOTA ROTANICAL STUDIES. 



sub-familv. The whole group niinil)ers only four species and is 

 thus, with tlie exception of the Pistioidcac, the smallest sub-family 

 in the Araccac. 



According to the recent monograph quoted from above, the 

 Calloideae occupy a place half way between the Pothoidcae and 

 the PhUodendroideae. The present writer admits altogether too 

 limited a knowledge of exotic aroids to pass judgment upon the 

 naturalness of such a classification. As to the interrelationships 

 of the various genera within the Calloideae it does not seem that 

 Engler's system is consistent. 



The one characteristic which is regarded as of great system- 

 atic significance, and practically the only one that could justify keep- 

 ing these genera together in the same sub-family, is the presence 

 of simple or unbranched latex ducts in connection with the 

 phloem of the vascular bundles. In Calla and Oroiitiitni these 

 ducts show up very clearly in fresh material, especially after 

 treatment with potassium bichromate, but they occur in neither 

 Syjiiplocarpus nor Lysichiton. Both fresh and preserved material 

 of both genera has been repeatedly examined but no trace of 

 them has ever been found. Scattered tannin cells which stain the 

 same way as the latex ducts with potassium bichromate are fre- 

 quently found in various parts of the cortex in all the genera of 

 the Calloideae, but no special significance has ever been accorded 

 to these. 



If a great deal of importance is to be attached to the pres- 

 ence or absence of these latex ducts then both Syuiplocarpus and 

 Lysichiton must be separated from Calla and Orontium in the 

 Calloideae and brought into some other position in the system. 

 Symplocarpus and Lysichiton no doubt are more closely related 

 to each other than they are to the other genera of the sub- 

 family. This relationship will be considered more in detail. 



The flowers are monoclinous in both genera and are built on 

 the same plan. The perianth and androecium each consist of two 

 dimerous cycles or whorls. In Lysichiton the ovary is two-celled 

 with a single ovule in each cell. The ovule grows out exactly 

 in the middle of the septum and is partly bent with the micro- 

 pyle towards the base of the chamber. In Symplocarpus one cham- 

 ber occurs in the ovary with a single orthotropous ovule pendant 

 from one side of the upper part of the cavity. In both genera 



