1068 Stephens . — The Stmccture and Development of the 
closely, haustoria grow out from the Striga root and penetrate that of the 
maize. In Fig. i is shown (in optical section) a root of Striga which has 
run parallel to a maize root for a short distance, and has developed a row 
of haustoria penetrating the maize. Fuller figures 1 part of a shoot of 
Sti'iga showing the connexion between its underground root-system and 
that of the maize, but his figure makes the Striga shoot apparently end in 
a tap-root, an error which is corrected in Burtt Davy’s copy 2 of Fuller’s 
plate. Fuller also gives 3 several diagrammatic sketches of sections of the 
haustoria, but no details of their structure or development have yet been 
published. It is the object of the present investigation to supply these 
details. 
The Haustorium. 
(a) General Structure. 
Compared with the haustoria of other phanerogamic parasites, that of 
Striga is comparatively simple in structure. Typically, it is almost globular 
in outline (PI. XCIII, Fig. i), and consists mainly of a mass of transparent 
nucleated cells which, following the usage of other writers, I will refer to as the 
‘nucleus’ 4 (;/., Figs, i, 5, 6). This is surrounded by a cortex of varying 
thicknesses (c., Figs. 1, 5, 6 ). Down the centre of the ‘nucleus’ runs a 
strand of tracheides, linking the vascular system of the parasite to that of 
the host ( a.s.t Figs. 1, 5, 6). This strand can be most clearly seen in 
Fig. 5, which shows an optical longitudinal section of a young haustorium 
which has penetrated into a maize root as far as the endodermis. This 
haustorium still retains the lenticular shape characteristic of its earlier 
stages, being at the most only six cells deep back to front. Its trans- 
parency thus enables its structure to be studied in optical section, though 
the outlines of the cells of the ‘ nucleus ’ at the median focus of the figure 
are obscured by those lying above, so that only a few were seen with 
sufficient clearness to be drawn in. They can be better seen in Fig. 6, 
which shows an older haustorium (which has attained its full size and 
globular outline) cut in a plane transverse to both mother root and haus- 
torium. This section is slightly oblique to the axis of the haustorium, 
so that the connexion of the axial strand of tracheides with the vessels of 
the mother root is not seen. 
(< b ) Origin and Early Development. 
The chief interest attaching to these haustoria lies in the fact that 
the very delicate and transparent nature of the parent root and young 
haustorium enables the origin and development of the latter to be studied 
1 Fuller (’01), PI. V. 2 Burtt Davy (’04), PI. LXXIV A. ' 3 Fuller, loc. cit. 
4 Barber (’06), Benson (’10). Fraysse (’06) refers to this tissue as ‘noyau meristematique central’ 
or ‘ masse meristematique centrale Other writers give it no special name. 
