How is 'intercalary' defined in a bacterial context, does have to do anything blank or dead cells of Spirogyra?
To define, intercalary differentiation or mitosis applies to any cytogenesis through mitosis which arises between different specialised tissues or cells. Spirogyra may undertake either sexual reproduction, should conditions prove to be adverse, or asexual. The latter involves an 'intercalary mitosis'. This entails a fragmentation in the original filament in order to produce additional filaments.
Within bacteria, a good analogy may be the 'Blue-Green algae', a deceptive misnomer for phototrophic cyanobacteria. Thus, in the context of filamentous bacterial colonies, you may consider intercalary binary fission, cell division within the filament.
More information available from: http://bioweb.uwlax.edu/bio203/2010/fenske_megh/reproduction.htm