R data.tree图中的标签方向

Question

使用下面plot.Node手册页中的示例，是否可以更改节点中标签的方向？默认情况下，它们显示为水平，并且似乎没有任何选项可以更改样式调用中的角度。理想情况下，我希望以30度的选定角度显示它们，但即使是垂直方向也可以达到目的。

library("data.tree")
data(acme)
SetGraphStyle(acme, rankdir = "TB")
SetEdgeStyle(acme, arrowhead = "vee", color = "blue", penwidth = 2)
#per default, Node style attributes will be inherited:
SetNodeStyle(acme, style = "filled,rounded", shape = "box", fillcolor = "GreenYellow", 
             fontname = "helvetica", tooltip = GetDefaultTooltip)
SetNodeStyle(acme$IT, fillcolor = "LightBlue", penwidth = "5px")
#inheritance can be avoided:
SetNodeStyle(acme$Accounting, inherit = FALSE, fillcolor = "Thistle", 
             fontcolor = "Firebrick", tooltip = "This is the accounting department")
SetEdgeStyle(acme$Research$`New Labs`, 
             color = "red", 
             label = "Focus!", 
             penwidth = 3, 
             fontcolor = "red")
#use Do to set style on specific nodes:
Do(acme$leaves, function(node) SetNodeStyle(node, shape = "egg"))
plot(acme)