1897.] 



NATURAL SCIENCES OF PHILADELPHIA. 



175 



Fig. 1. 



Examining next some plants of Triphasic/, trifoliata which had 

 wintered in the open air, I was pleased to find the leaf origin of 

 these spines confirmed. The articulation, which the leaves of most 



of the Citrus tribe have near the junction 

 of petiole and lamina, is plainly seen in 

 these spines (Fig. 1). The part above the 

 articulation is completely dead and brown 

 as one might expect the lamina of a leaf to 

 be — the more highly vitalized spine, the 

 metamorphosed petiole, has resisted the 

 frost killing severity of the winter. 



We can thus see that the proper classi- 

 fication of the spine in the Citrus tribe is 

 with such as are borne by thistles or sim- 

 ilar plants, where the leafy bracts form- 

 ing the involucres terminate in sharp 

 rigid prolongations, which are not to be classed with spines equally 

 with the sharp apices of Gleditschia, Madura and other specifically 

 spiny species. 



FLOWERS AND FLOWERING OF LAMIUM PURPUREUM. 



One might suppose that a plant so widely spread over the world, 

 and one that intrudes itself so persistently on every one's attention as 

 Lamium purpureum, could not possibly have anything written about 

 it that would be new to botanists. But I am inclined to believe that 

 plants have not a uniform behavior in every place, and possibly the 

 behavior of species here may be different from that in the Old World. 

 These considerations make it the more important that the points I 

 have noted in the plants growing on my grounds should be placed 

 on record. 



The species is very abundant as a weed on my grounds near 

 Philadelphia. It is the form with the smaller flowers and without 

 the ring of hair below the throat that is described in the typical 

 form of Europe. It was originally introduced into my grounds 

 from Germany. It is probably the form which Willdenow regards 

 as a good species, and describes as Lamium ineisum. The hair that 

 is found in the throat of L. purpureum is absent — there is but a 

 single short tooth instead of two on the lower lip, and the pollen is 

 orange instead of bright scarlet. 



Dr. Bromfield notes " anthers with several tufts of stiff hairs or 

 bristles on the face of each cell, and according to Mr. Leighton ac- 



