290 PROCEEDINGS OF THE ACADEMY OF [1893. 



study of the plant at Seal Harbor, Maine, on July 9th seemed to 

 make its peculiarity clear. 



It may first be noted that when a leaf starts from its parent stem 

 we may look for a bud in the axis. If a leaf be present without an 

 axillary bud, Ave conclude that there has been or ought to have 

 been one, and look for some reason for the seemingly abnormal con- 

 dition. 



As already noted by the author, the common peduncle opposite 

 to a leaf in Boraginaceous and other plants, means simply that the 

 arrested axis has been pushed aside by the strongly developed 

 growth of the axillary bud, which then assumes the leadership until 

 " history repeats itself," and it also is pushed aside to make Avay for 

 a new leader. But Mertensia maritima does not seem to follow this 

 rule, and seems wholly exceptional. Everything proceeds for 

 awhile in the usual way. The leaves are all alternate as a well- 

 behaved Boraginaceous plant should be. But when in the flower- 

 ing stage there are a pair of opposite leaves, and at the same node, 

 three branches — one bearing flowers, and the other two continuing 

 each an axial growth. How is it possible that three axial growths 

 should have been developed from only a pair of leaves ? 



When these leaves are carefully examined, however, the axillary 

 buds are found to be still there. They have not followed the Bor- 

 aginaceous habit of pushing at once into growth, and, assuming 

 leadership, pushing the parent shoot aside. The pair of leaves are 

 not exactly opposite, and the branch bearing the flowers seems to 

 occupy a space of its own on the stem, between the pair of leaves. 



Dicotomous Branching in Spergularia media. 



Noting that every flower was abundantly fertile, and suspecting 

 from this fact self-fertilization, investigation followed and it was 

 found that the pollen is shed just at the time of opening, thoroughly 

 covering the stigmas, and absolutely insuring self-fertilization. 



Comparing the inflorescence with some Boraginacese nearby, 

 along the coast at Seal Harbor, an interesting lesson is taught as to 

 how the dichotomous arrangement is produced from the opposite 

 leaved, and the extra-axillary from the alternate leaved character, 

 respectively. In Spergularia media, when the arrestation of axial 

 growth occurs previous to the advent of the floral condition, the 

 next pair of axillary buds start at once into growth and we 

 thus have two actual centers of axillary growth, the arrested 



