P2 Mr. Brown's Observations on the 



It is also known that in a compound spike, while the expansion 

 of each partial spike is ascendent, that of the spikes, with relation 

 to each other, is descendcnt; the terminal spike expanding first, 

 and the others in a regular succession downwards. This order, 

 indeed, admits of a greater number of exceptions than that of 

 tlie simple spike; several of them apparently depending on the 

 density 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*. 



The simple racemus and corymbus are obviously very slight mo- 

 difications of the spike, and in their expansion obey the same law. 



A syngenesious compound flower, or capituluni as it may be 

 termed, is merely a spike with a shortened and generall}' de- 

 pressed axis. In cases where this capitulum is unquestionably 

 simple, the expansion of its flowers is uniformly from circum- 

 ference 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 ob- 

 served ; their expansion with relation to each other being from 

 centre to circumference. In their denser aggregations, whether 

 Ibrming a compound spike or head, the same order of expansion 

 obtains, and it continues though the florets in each common calyx 

 or involucrum should be lessened in number, or even reduced to 

 unity, as in Echinops and Rolandra. 



* The most remarkable exception to the order of the compound spike exists in the com- 

 pound umbel of Umbelliferae, of which the outer umbellulae expand somewhat earlier than 

 the central j and as this order of expansion seems to extend through the whole natural 

 family, Astraiitia, in which the terminating umbel expands much earlier than those of the 

 lateral branches, cannot be considered as having a compound umbel. 



The 



