CH. IV] OPPOSITE AND ALTERNATE BUDS 31 



It is the rule where buds, leaves, &c., are opposite, 

 that each alternate pair is directed at right angles to the 

 pairs immediately above and below on the twig, and 

 this decussate arrangement, as it is termed, prevails in 

 all the genera in the above list. Cases occur, however, 

 where buds which are not truly opposite, or not consist- 

 ently so, but so nearly so as to be termed sub-opposite, 

 are not always at the same time decussate. Examples 

 are afforded by 



Picea excelsa Rhamnus catharticus 



Abies pectinata Salix pur pur ea. 



In some of these cases, indeed, the buds, though 

 strictly speaking not inserted at the same level, appear 

 to be so arranged in whorls, or groups clustered round the 

 stems in a radiating manner, that the shoots to which 

 they give rise present the appearance of being in verticels, 

 or regular tiers, at definite intervals. It is to this that 

 the pseudo-whorls or false verticels of the following are 

 due : 



Pines Spruces Silver Firs, 



and, in a less pronounced degree, a similar arrangement 

 occurs in 



Larch Ash Oak 



Cherry Bird Cherry Holly. 



In the following, the buds are alternate, that is to say 

 each bud stands isolated at its own node, the insertions 

 being either alternately right and left of the twig bear- 

 ing them, so that they are two-ranked (distichous) if 

 regarded as to the vertical series formed by joining all 

 the buds up the twig standing one over the other; or 

 there are three or five such vertical series or ranks. In 

 this latter case, a line joining each and every bud-inser- 

 tion in succession would pass more or less spirally round 



