78 MORPHOLOGY OF IRREGULAR FLOWERS. [BOOK i. 



In the Labiates, the corolla of Lamium garganicum when 

 it first becomes visible, is represented by a little cupula 

 scarcely hollowed out at all, bordered by five teeth which are 

 very short, and at this time alone, quite equal, for two of 

 them speedily cohere and become blended together to form a 

 large, round, and very convex lamella, which subsequently 

 becomes the helmet of the Lamium. Of the three remaining 

 teeth, the central one also becomes much larger than the 

 others, which are always small and atrophied. The evolution 

 of the didynamous stamens exposes the singular fact, that 

 the larger two originate rather before the other two, which 

 they exceed in length at every period of their development. 

 Among other Labiates, Ajuga reptans, Scutellaria Columnse 

 and commutata present us with the same phenomena. In 

 Phlomis fruticosa the helmet is formed of two segments of 

 the corolla, as in Lamium. In the Scrophulariacese the 

 segments of the nascent corolla are also equal, but only at 

 their origin. The inequality always manifests itself very 

 soon, and earlier in proportion to the subsequent irregularity 

 of the corolla (Antirrhinum majus, Linaria cymbalaria, 

 Pentstemon Scouleri, Collinsia bicolor, Scrophularia verna). 

 In the genera which possess a fifth, supplemental stamen, 

 this is formed at the same time as the two smaller, and in the 

 spot which remains vacant in the Labiates. The symmetry 

 is then perfect. In the Birthworts (Aristolochia Clematitis 

 and Pistolochia), the simple perigone composing the flower 

 is, at its origin, a kind of tube, very short, at first with an 

 equal and as it were truncated border ; but this state per- 

 sists but a very short time. One side of the mouth of the 

 tube becomes much developed, so as to form the well-known 

 limb of the Aristolochias, while the other undergoes but 

 slight expansion. 



In the Verbenes (Verbena urticaefolia), and in the Dipsaceae 

 (Scabiosa ucranica and atropurpurea), the irregular corolla 

 follows the same law of development. 



The petals of Leguminous plants are equal and alike at the 

 origin of the flower ; but a difference of form and size very 

 soon becomes evident (Cytisus nigricans and Laburnum, Ulex 

 europseus, Erythrina cristagalli) . The case is the same in the 



