137 



atmospheric conditions as are our Pacific species. At all events 

 the matter deserves further examination. 

 Stanford University, California. 



MUTUAL IRREGULARITIES IN OPPOSITE LEAVES 



By Francis E. Lloyii 



It is not uncommon to find that the leaves of the lilac (Syringa 

 vulgaris L.), which are generally supposed to present little varia- 

 tion in shape, become notched on one side. A tooth or a lobe 

 of considerable size may thus be formed, so that the simple 

 cordate leaf is then lobed asymmetrically. The lobe is some- 

 times of quite regular form and ends in a fine tooth at the tip. 

 It is moreover supplied with veins which give it a normal appear- 

 ance. At other times it is more rounded ; or there may be 

 nothing more to suggest it than a rounded irregularity on the 

 margin, accompanied by a slight warping of the leaf blade nearby. 



Now it has further been observed that when such an irreg-u- 

 larity occurs, the leaf opposite — the leaves being in decussating 

 pairs — has with few exceptions a similar lobing, but on the other 

 side of the midrib ; and therefore, since the ventral surfaces of the 

 leaves are opposed in the bud, on the same side of the axis of the 

 stem. A considerable number of similar instances have been 

 observed by me in some other plants with opposite simple leaves, 

 namely in Lonicera and Forsythia. What appears at first blush 

 to be a variation of the same kind may occur also in compound 

 leaves, and such a case I have found in the European ash, in 

 which the terminal leaflets of a pair of opposite leaves showed 

 mutual variations but in this case on the same side of the midrib. 

 In one of the leaflets a lateral lobe only was formed, while on 

 the other a complete lateral leaflet appeared in the corresponding 

 position. The condition recalls that which arises in the juvenile 

 opposite leaves of some plants {Phaseolus) and in the alternate 

 leaves on the new shoots of others {Rub us occidentalism R. nigro- 



some cases rarely, if ever, uncovered. Farther north on the Atlantic coast, Fucus 

 edentatus De la Pyl. and F. serratus L. are found near the low-water mark and do not 

 as a rule become very dry at the ebbing of the tide. — Ed.] 



