Table 1.

Comparison of intracellular processes involved in the growth and branching of N. crassa in open and constraining environments

Growth	Hypha	Spitzenkörper	Microtubules
Nonconstraining geometries
Single hypha	Profile: Parabolic, laterally symmetrical	Location and dynamics: Central, at the hyphal apex; permanently present	Orientation: Parallel to axis Distribution: Axially symmetrical Dynamics: Population relatively constant
	Source: Agar (65–67)* and CNC*	Source: Agar (68)* and CNC*	Source: Agar (43–45)* and CNC*
Lateral branching	Occurrence: Statistically regular Angle: ∼45° Profiles: Parabolic for parental, daughter hyphae Apical extension: Reduced during branching	Location and dynamics: Central, at the hyphal apices; permanently present in parental hypha; early appearance in the daughter hypha	Orientation: Parallel to hyphal axes Distribution: Axially symmetrical Dynamics: Population relatively constant
	Source: Agar (21)* and CNC*	Source: Agar (21) and CNC*	Source: Agar (21) and CNC*
Apical branching	Occurrence: Regular, but rare Angle: V-shaped, ∼45° Profiles: Initial round-up for the twin hyphae Apical extension: Reduced during branching	Location and dynamics: It retracts from the apex and disappears; then, two Spitzenkörper centers emerge at the centers of hyphal apices	Orientation: Parallel to hyphal axes Distribution: Axially symmetrical Dynamics: Population relatively constant
	Source: Agar (21)	Source: Agar (21)	Source: Agar (44, 74)
Constraining geometries
Nestling	Occurrence: Triggered by contact at acute angles Angle: Change of direction as dictated by the wall Profiles: Skewed off-axis, toward the wall Apical extension: Unchanged	Location and dynamics: Off-axis location, pressing against the obstacle; return to central position after passing the obstacle	Orientation: Aligned off-axis Distribution: Axially asymmetrical, “cutting corners” Dynamics: Population relatively constant
Hit & split	Occurrence: Triggered by near-orthogonal collisions Angle: T-shaped, at ∼180° Profiles: Triangular; then, progressively parabolic Apical extension: Constant during splitting	Location and dynamics: It disappears during splitting of parental hypha; then, two Spitzenkörper centers form centrally at the apex of twin branches	Orientation: Random close to the splitting Distribution: Random close to the splitting Dynamics: Substantial dissolution; then, formation in twin hyphae
Branching in/after tightly constraining channels	Occurrence: Triggered by free space for branching Angle: Dictated by geometry Profiles: Parabolic for parental hypha; circular, then increasingly parabolic for daughter hypha Apical extension: Constant during branching	Location and dynamics: Parental Spitzenkörper progresses unchanged; the daughter hypha forms its own Spitzenkörper early and centrally	Orientation: Parallel to the hyphal axes Distribution: Axially symmetrical Dynamics: Populations relatively constant

CNC, confined, but nonconstraining.

^*Present study.