Abstract
The detachment of root caps was examined microscopically, using rice crown roots grown by "leaf-cutting" method. An agar-immersion process was newly introduced to secure tissues from sloughing off during microtome-sectioning procedures. Root caps of just-emerging crown roots are designated here as "primary root caps". Their structures are characterized by predominantly stratified cell layers, arranging parallely to the tip surfaces. Contrastively, the structures differ from those of the later appearing, ordinary root caps with well defined cell files, i.e. columella. Within several days after their emergence, the "primary root caps" tended to dissociate and detach from root tips. The ways of their detachment were classified into the following three types; (1) the "cylindrically-detaching" type, (2) the "penetratedly-detaching" type, and (3) the "falling-off" type, respectively. In the former two types, detached cell layers remaining on the basal parts suppressed the outgrowth of root hairs and lateral roots. Following the detachment of the "primary root caps", in the "denuded" ordinary root caps, the falling at the tips of single cells or small cell groups seemed to be prevalent. The mechanism of the detachment of the "primary root caps" may be attributed to the mutual dissociation of their cell layers due to their different growth rates, and also to the collapse of their cell layers at the tips due to the development of columella.
