THE ANGIOSPERMAE 



1503 



which is incapable of germination. The percentage of such seeds varies 

 between different genera and between different samples of seed, causing 

 great irregularities in the germinable capacity. Out of 54 lots of Carrot seed, 

 an average of 16 per cent, were embryoless, the maximum being 37 per cent. 



Fig. 1377. — Sagittaria sagittijolia. Alismaceat-. Section 

 of the campylotropous ovule with embr\o. The 

 cotyledon is at the top, the erowing point is seen at the 

 right-hand side. The imperfect endosperm disappears 

 as the seed matures. 



In Parsley the average was 20 per cent., while in Fennel {Foeniculum vul- 

 gare) the average was 34 per cent., with the maximum at 58 per cent. There 

 is no suggestion that this is the result of disease, but it has been shown that 

 infestation by Lygiis bugs raises the incidence of embryolessness and a 

 similar infestation is known to affect adversely the pollination and seed 

 setting in Alfalfa [Medicago sativa). 



The culture of seed embryos excised at an early stage of development 

 is a technique of recent growth which offers great practical benefits to the 

 plant breeder, since embryos of certain types of hybrid which do not survive 

 in the seed can be successfully reared into plants if cultivated artificially. 

 Furthermore long periods of dormancy can be avoided. 



