OF PLANTS CALLED COMPOSITE. 273
to make a few remarks on the more usual modes of inflo- rescence.
It is well known that in an absolutely simple spike the expansion of the flowers is ascendent ; that is, begins at the base of the spike and proceeds regularly upwards. To this order very few real exceptions occur, several of the apparent deviations being connected with some degree of composition in the spike.
It is also known that in a compound spike, while the [92 expansion of each partial spike is ascendent, that of the spikes, with relation to each other, is descendent ; the ter- minal spike expanding first, and the others in a regular succession downwards. This order, indeed, admits of a greater number of exceptions than that of the simple spike ; several of them apparently depending on the den- sity or imperfect composition of the spike ; and the more usual deviation consisting in the expansion beginning below the apex, and proceeding in opposite directions from the point of commencement ; the upper portion following the order of the simple, the lower that of the compound spike. 1
The simple racemus and corymbus are obviously very slight modifications of the spike, and in their expansion obey the same law.
A syngenesious compound flower, or capitidum as it may be termed, is merely a spike with a shortened and generally depressed axis. In cases where this capitulum is unquestionably simple, the expansion of its flowers is uniformly from circumference to centre, or in the order of the simple spike. Where the capitula are disposed in a corymbus, which is their usual mode of combination, the order of the compound spike is observed ; their expansion with relation to each other being from centre to circum- ference. In their denser aggregations, whether forming a
1 The most remarkable exception to the order of the compound spike exists in the compound umbel of Umbellifera?, of which the outer umbellultc expand somewhat earlier than the central; and as this order of expansion seems to extend through the whole natural family, Astranlia, in which the terminating umbel expands much earlier than those of the lateral branches, cannot be con- sidered as havinff a compound umbel.
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