41, C), where, however, there is a further complication in the form of an adventitious envelope or ectotheca (ect.) split off from the gonophore as a protective covering, and not present in Cladocoryne.
While the stele of the primary root in both Gymnosperms and Angiosperms is usually diarch or tetrarch, the large primary root-steles of many adventitious roots are frequently polyarch, sometimes with a very large number of protoxylems. Such a stale seldom has the centre filled up with xylem, this being replaced by a large-celled pith, so that a siphonostelic structure is acquired (fig.
Adventitious roots, arising from stems, usuall) take origin in the pericycle, but sometimes from other parts of th Conjunctive.
Bruising by a cartwheel, insects-having started a callus on which adventitious buds arise, or to the destruction of buds at an early stage.
When we come to phenomena such as proliferations, vivipary, the development of Lammas shoots, adventitious buds, epicormic branches, and to those malformations of flowers known as peloria, phyllody, virescence, &c. while assured that definite, and in many cases recognizable, physiological disturbances are,at work, we find ourselves on the borderland between patho~gical and physiological variation, where each case must be examined with dtie regard to all the circumstances, and no generalization seems possible beyond what has been sketched.