148 



HARDVVICKE'S SCIENCE-GOSSIP. 



the axis, but also the order in which they open, and 

 this is called their evolution. We must remember 

 that in all cases a flower-bud is like a leaf-bud ; and 

 that the flowers, like the leaves, arise from the axis in 

 one of two ways : that is to say, the buds are either 

 produced in the angle formed by the inclination of a 

 leaf to the stem (axillary), or else they arise from the 

 termination of the axis (terminal). But in the axillary 

 mode of inflorescence the leaf which forms the angle 

 with the axis is called a bract. In many cases these 

 bracts are not to be distinguished from leaves, and 

 their structure is similar. Such instances occur in the 



from below upwards — those situated lowest expanding 

 first, the axis itself being carried on indefinitely. Thus 

 the expansion of the flower is centripetal — centre- 

 seeking. The simplest form of the inflorescence is 

 seen in the currant, fumitory, &c. In this the pedicels 

 (secondary axes) are of equal length, and each has a 

 bractlet at its base. The corymb is simply a slight 

 modification of the raceme — the lower pedicels being 

 longer than the upper ones, and thus forming a more 

 or less flattened surface. It should be noticed that an 

 inflorescence which at first appears to be corymbose, 

 may ultimately become racemose — e.g. in Crucifera;. 



Fis 



119. — Forget-me-not (Myosotis palustris), showing 

 scorpioid inflorescence. 



periwinkle (Vinca), pimpernel (Anagallis) &c. But 

 in other cases these bracts assume a very different 

 appearance, so that even the most superficial observer 

 would notice the want of resemblance to true leaves. 

 Spathes, glumes, the involucre of Compositse and 

 scales are all so many modifications of bracts, and it 

 should be borne in mind that all these are but 

 different forms and arrangements of leaves — the leaf 

 being the morphological type on which the whole 

 structure of the flower is founded. It is noticeable, 

 in passing, that the presence or absence of bracts 

 constitutes a valuable classificatory medium. Now, as 

 has been mentioned above, flowers are either axillary 

 or terminal in their relation to the axis. And it is this 

 relation which gives origin to the two great divisions 

 of inflorescence : indefinite and definite. In the former 

 division the axis gives off axillary buds, which expands 



Fig. 120. — Comfrey (Symphytum officinale), showing scorpioid 

 inflorescence. 



The umbel is another form of this inflorescence, the 

 primary axis being shortened, and the secondary axes 

 coming off from the same points (radii), so as to be 

 nearly equal in length. 



Notice also the bracts forming the involucre and 

 involucel in Umbelliferse. There is a term to which 

 different meanings have been attached by different 

 writers — the panicle. Perhaps the best definition of 

 a panicle would be an inflorescence in which the 

 secondary axes give rise to tertiary ones which bear the 

 flowers. But it is frequently used to express a totally 

 different kind of inflorescence (the definite), and, like 

 all terms which are ambiguous, has become unsuited 

 to the requirements of true science. The spike is simply 

 a sessile raceme, and the spadix a succulent spike. 



