234, POPULAR FIELD BOTANY. 
TETRADYNAMIA. SILIQUOSA. 
THALAMIFLOR2. CRUCIFER2X. 
SINAPIS. (Musrarp.) 
Generic Character. Calyx spreading, that is, the parts not 
joined together, but standing apart. Flower yellow. Pod two- 
valved, and ribbed, very slender. Seeds in one row. 
SINAPIS ARVENSIS. (Plate XIV. Fig. 55.) Wald Mustard 
or Charlock. This is one of the species of Mustard, though 
not that used as such for the table, but they all have the 
same pungent quality. It grows from one to two feet high, 
has large, rough leaves, and yellow flowers, which are also 
rather large; pod with many angles, and showing the form 
of the seeds it contains. It is troublesome to the farmer, 
springing up in his fields in great quantities. In Sussex, 
when a field is left uncultivated for a short time, it is sure 
to be covered with Charlock. This is particularly the case 
with those situated on the chalky downs. 
Stnapis ALBA. White Mustard. This is the plant which 
in a young state is eaten as Mustard with Cress. It is very 
similar to the last; but has a long sword-shaped beak at 
the top of the pod, and does not flower so early. 
Srnapis Nigra. Common Mustard. The seeds of this 
