248 



ABSORBING SYSTEM 



still further augmented by active growth on the part of the epithelial 

 elements themselves. The resulting elongation is often very consider- 

 able. The average length of the epithelial cells of Wheat, for example, 



Fig. 96. 



Scutellum (haustorial organ) of a seedling of Briza minor ; the absorbing tissue 

 resembles the piliferous layer of a root. 



is '023 mm. in the resting condition, but rises to '09 mm. during the 

 period of most active absorption ; for Maize the corresponding figures 

 are '025 mm. and '071 mm. When fully developed, the absorbing cells 



of the scutellum thus generally appear as 

 blunt elongated sacs or tubes, which are from 

 four to twelve times longer than their 

 breadth. As might be expected, the walls 

 of these cells are very thin ; another charac- 

 teristic feature is the abundance of their 

 protoplasmic contents. The nucleus usually 

 lies near the base of each cell. When ger- 

 mination is completed and the endosperm 

 entirely exhausted, the absorbing cells col- 

 lapse ; their lateral walls crumple up and the 

 protoplasmic contents disappear altogether. 



The author has shown that the scutellar 

 epithelium of Briza minor displays a remark- 

 able resemblance to the absorbing tissue of 

 an ordinary root (Fig. 96). Before germina- 

 tion begins, the absorbing cells are roughly 

 cubical (with an average diameter of '017 

 mm.) ; when the plumule of the seedling has 

 reached a height of 3 mm., these cells may 



^SAaSiJS^&^S^L be ' 086 mm - lon s> while the ^ finall y avera s e 



or g ln" 01 ' bing cells f the haustorial as much as ' 15 mm - in length. Here, 



moreover, the absorbing tubes arise by local 

 prolongation of the superficial cells of the absorbing organ, just as is 

 the case with typical root-hairs. The fully grown scutellum presents a 



Fig. 97. 

 A. Seedling of Tradescantia erecta : 



