E. R. Saunders 151 



being hoiverer nun-effective unless combined ivit/i the fonner. Having 

 brought our consideration of the inter-relations of hoary and glabrous 

 to this point, we can now proceed to consider the rcl.itions of these 

 types to the half-hoary form. 



The characteristic features of the half-hoary foi-iii have been 

 described above (p. 146). It may be added that this type is peculiar 

 in that the adult appearance is not assumed from the beginning as is 

 the case witii the fully hoary and glabrous types. As a rule the first 

 leaf after the cotyledons has only quite a few hairs on the basal and 

 extreme apical margins. The succeeding leaves exhibit an increasing 

 degree of hairiness until about leaf 5 when the half-hoary condition is 

 generally reached and thenceforward maintained, except that in the 

 axillary buds a similar grading may be repeated, one or two of the first 

 young leaves, especially if rather stunted, being very slightly hairy, the 

 succeeding ones typical. In this behaviour we are reminded of another 

 Crucifer, Biscutella laevigata, in which hairy, intermediate and glabrous 

 forms are found. In Biscutella as in Matthiola transition stages from a 

 juvenile to a stable adult condition — stages which may sometimes be 

 witnessed again in an axillary shoot — commonly occur in the inter- 

 mefliate plants, but in the case of Biscutella the gradation is from the 

 partially hoary towards the glabrous condition ; in the half-hoar}' Stock 

 it is in the opposite direction — towards the fully hoary condition'. This 

 return in the axillary shoot to a gi'ade represented at a lower level on 

 the main axis is curious but not uncommon in plants. It is not confined 

 to the period of vegetative development ; it may equally be observed in 

 flowering shoots as, e.g., in Digitalis 'purpurea van heptandra and in 

 Erodium pimpinellifolium. In D. heptandra as described elsewhere'' 

 there is a gnidual transition up the spikes fi'om a more extreme 

 heptandrous condition towards the normal until the end of the flowering 

 season when the flowers often show a slight retrogression towards the 

 abnormal condition. In the axillary shoots the starting-point is usually 

 some intermediate stage in the series — one which has already been 

 passed through by the main axis at the time that the axillary shoot 

 begins to flower. 



In Erodium pimpinellifolium the flower is commonly described as 

 having the two postero-lateral petals distinguished from the other three 



' Fuller details are given in an account of observations "On a discontinuous variation 

 occurring in Biscutella laevigata," Proc. Roy. Soc. Vol. LXii. 



- " On Inheritance of a Mutation in the Common Foxglove {Digitalis purpurea),'' The 

 New Plnjtologist, Vol. x. 1911, p. 54. 



